                                    DATA USERS GUIDES

        1:   Digital Line Graphs from 1:24,000-Scale Maps
        2:   Digital Line Graphs from 1:100,000-Scale Maps
        3:   Digital Line Graphs from 1:2,000,000-Scale Maps
        4:   Land Use and Land Cover Digital Data from 1:250,000- and
             1:100,000-Scale Maps
        5:   Digital Elevation Models
        6:   Geographic Names Information System
        7:   Alaska Interim Land Cover Mapping Program

Data Users Guides generally replace the Geological Survey Circular 895.

Questions regarding availability and ordering of US GeoData (all types of
digital cartographic and geographic data produced and distributed by the U.S.
Geological Survey) should be addressed to:

        Earth Science Information Center
        U.S. Geological Survey
        507 National Center
        Reston, Virginia  22092
        (703)648-6045 / 1-800-USA-MAPS

Technical questions and comments should be addressed to:

        Office of Technical Management
        U.S. Geological Survey
        510 National Center
        Reston, Virginia  22092





                            UNITED STATES
                     DEPARTMENT OF THE INTERIOR
                       U.S. GEOLOGICAL SURVEY




            DIGITAL LINE GRAPHS FROM 1:100,000-SCALE MAPS


                                                                          

                         Data Users Guide 2



































                          Reston, Virginia
                                1989











































                        First printing, 1985
                   Second printing (revised), 1989






                              CONTENTS
                                                                   Page

Introduction ......................................................   1
Data collection ...................................................   2
Data content ......................................................   3
Data structure ....................................................   4
        Levels of structuring .........................................   4
        Topology ......................................................   5
        Topological elements ..........................................   5
Attribute codes ...................................................   6
        Major attribute codes .........................................   7
        Minor attribute codes .........................................   8
        Sample attribute codes ........................................   8
Sample line graph structure .......................................   9
Graph theory in DLG data ..........................................  12
        Area case .....................................................  12
        Network case ..................................................  12
        Area-hybrid case ..............................................  12
Distribution formats ..............................................  19
Source materials ..................................................  19
Cell size and file extent .........................................  20
        Preliminary data ..............................................  22
Coordinate systems ................................................  23
        Standard distribution format ..................................  23
        Optional distribution format ..................................  24
Data validation ...................................................  24
Appendix A.  Standard DLG distribution format (record contents) ...  28
         B.  Optional DLG distribution format (record contents) ...  42
         C.  Map projection parameters ............................  60
         D.  DLG attribute codes ..................................  62
         E.  Coordinate conversion ................................  79
         F.  Sample DLG data file (standard distribution
                           format) .........................................  80
         G.  Sample DLG data file (optional distribution
                           format) .........................................  85

                                          

                            ILLUSTRATIONS
                                                                   Page

Figure l.  Map elements showing roads, railroads, buildings,
                         streams, and lake and forest areas ................   6
       2.  Sample line graph ......................................  10
       3.  Window from the Cartersville, Ga., 1:100,000-scale
             USGS quadrangle map ..................................  13




                                 iii
                      ILLUSTRATIONS--continued
                                                                   Page

Figure 4.  Plot from line graph of hydrography, Cartersville,
                Ga., 7.5-minute section of quadrangle ................  14
       5.  Sectioning scheme for DLG data of a 1:100,000-scale
             quadrangle ..........................................  22

                                          

                               TABLES
                                                                  Page

Table 1.  Major codes used for DLG base categories ...............   7
      2.  Digital description of example DLG-3 ...................  11
      3.  Selected sample of standard format DLG-3 records
            of Cartersville, Ga., 7.5-minute section of
            quadrangle ...........................................  15
      4.  Standard and optional DLG format .......................  20




































                                 iv




            DIGITAL LINE GRAPHS FROM 1:100,000-SCALE MAPS
                                                                          

                            INTRODUCTION

The Earth Science Information Center (ESIC) distributes digital cartographic/
geographic data files produced by the U.S. Geological Survey (USGS) as part
of the National Mapping Program.  Digital cartographic data files may be
grouped into four basic types.  The first of these, called a Digital Line Graph
(DLG), is line map information in digital form.  These data files include
information on planimetric base categories, such as transportation, hydrography,
and boundaries.  The second form, called a Digital Elevation Model (DEM),
consists of a sampled array of elevations for ground positions that are usually,
but not always, at regularly spaced intervals.  The third type is Land Use and
Land Cover digital data, which provides information on nine major classes of
land use such as urban, agricultural, or forest as well as associated map data
such as political units and Federal land ownership.  The fourth type, the
Geographic Names Information System, provides primary information for known
places, features, and areas in the United States identified by a proper name.

The digital cartographic data files from selected quadrangles currently
available from ESIC include the following:

   o    Digital Line Graphs (DLG's)
        --1:2,000,000-scale maps
        --7.5- and 15-minute topographic quadrangle series
        --1:100,000-scale quadrangle series

   o    Digital Elevation Models (DEM's)
        --7.5-minute quadrangle coverage
        --1.0-degree quadrangle coverage

   o    Land Use and Land Cover digital data
        --1:250,000- and 1:100,000-scale land use and land cover and
            associated maps
        --1:250,000-scale Alaska Interim Land Cover Maps

   o    Geographic names

This document describes the Digital Line Graphs (DLG's) prepared from the
1:100,000-scale materials associated with the USGS Topographic Map Series.  The
series will eventually provide complete national coverage.


                  
Any use of trade names and trademarks in this publication is for identification
purposes only and does not constitute endorsement by the U.S. Geological Survey.
The digital data are useful for the production of cartographic products, such
as base maps, and the data are structured to support the analytical functions of
geographic information systems.  A typical use of base category digital
cartographic data is to combine them with other geographically referenced data,
enabling various automated spatial analyses to be conducted.


                           DATA COLLECTION

The following is a general overview of DLG data collection methods currently in
use at the USGS.  Individual Mapping Centers may vary the details of data
collection, but the basic method and resultant DLG-3 files remain standard.

The USGS collects DLG data files using manual, semiautomatic, and automatic
digitizing systems.

The manual digitizing method is accomplished primarily on Altek and Intergraph
digitizing systems.  Stable-base manuscripts of the relevant data categories are
prepared from the original map separates.  The operator initiates digitizing
by fixing the manuscript to the digitizing table, and collecting registration
points for the corners of the quad.  Features and their corresponding attributes
are digitized as lines, nodes, or areas.  Both systems are capable of collecting
the topological elements and their associated codes concurrently; in addition,
the DLG processing software, PROSYS, is able to automatically place area
pointings for areas which carry no attribute codes.  The Altek digitizing
systems currently in use by the USGS are basically "blind" systems.  In order to
view the captured data the operator must generate plots or utilize a separate
graphics display terminal.  The Intergraph systems at the USGS allow for the
visual display of the digitizing in progress, interactive editing, and for
access to commonly used attribute codes.  When all positional and attribute
coding is complete, the digitized data file is processed through PROSYS
software, which builds the topology and identifies structural errors.  On the
Altek systems, coding and positional accuracy are verified using plots. The
Intergraph system allows for visual confirmation of most codes, but plots are
used for accuracy checks and for quality control in more complex areas.  After
the file has been corrected and reprocessed through PROSYS, it is entered into
the National Digital Cartographic Data Base (NDCDB) as a DLG-3 file.

The semiautomatic line-following method of collecting data is accomplished on
Laser-Scan systems.  This is an interactive line-following digitizing and
editing system.  Graphic data are captured in vector format and the line strings
interactively coded.  The primary application of the LaserScan equipment at
the USGS is to collect hypsography data.  The Lasertrak digitizer uses a film
negative that is a photographic reduction of the original source material.  The
reduction factor is dependent on the latitude of the quadrangle, the density
of the data, and photographic line reduction limitations.  Prior to each
digitizing session, the operator performs calibration and registration
procedures to ensure that digitizing accuracy is maintained.  The reduced film
negative is projected onto a large format display screen.  The operator selects
and codes the feature to be digitized, monitors the progress of the Lasertrak as
the feature is automatically collected in vector format, and intervenes when an
error occurs or when automatic line following is interrupted due to graphic
ambiguities.  The resulting vector file is processed to correct distortions
and to detect errors, and plots are produced to facilitate quality control and
editing. The Laser-Scan interactive Edit System allows for correction of
digitizing errors, paneling of adjacent sections, and for manual collection and
coding of categories of data which do not lend themselves to efficient line
following.  When editing is complete, the data are converted from Laser-Scan's
Internal Feature Format into PROSYS input format and processed through PROSYS to
build topology and identify structural errors.  After the data file has been
edited and reprocessed to correct errors, the DLG-3 file is entered into the
NDCDB.

The automatic method of collecting data is accomplished using Scitex raster
scanning and editing systems.  Graphic data are captured in raster format from
composites of selected map features, then edited, and reformatted into vector
data.  In preparation for scanning, a stable-base composite of the map separates
is prepared representing the data category to be collected.  Prior to scanning,
the manuscript is annotated in a prescan editing process to identify features or
locations which will require inspection by the Scitex operator.  The scanned
raster data file is manipulated interactively and in batch mode on the Scitex
Response color edit station.  The first editing operation (postscan edit) is a
general cleanup.  The interactive editing is facilitated by automatic search
routines which present the operator with the problem areas identified in the
prescan edit.  The linework is then skeletonized (thinned to a centerline of
one-pixel width).  A one-pixel gap is made in the linework at the locations of
attribute change annotated during the prescan edit.  These breaks in the
linework mark the positions for node placement during structuring.  Linear
features symbolized by dots or dashes are changed to a continuous line, and
point features, such as wells and rocks, are changed to single points through
interactive edit and batch procedures.  When line editing is complete, the
raster files are vectorized.  Complete or partial feature coding is accomplished
using the manual and semiautomatic coding capabilities of the Scitex edit
stations.  The files are then processed through PROSYS to build topology and to
identify structural errors.  Files which were only partially coded on the Scitex
are sent in DLG format to Intergraph stations for coding completion.  Quality
control plots are generated to check positional and coding accuracy; the
corrected files are then reprocessed through PROSYS and entered into the NDCDB
as DLG-3 files.


                            DATA CONTENT

The DLG data files derived from the 1:100,000-scale maps contain selected base
categories of cartographic data in digital form; these data categories do not
necessarily correspond to the traditional feature separates associated with the
maps.  The following categories are included in current 1:100,000 DLG files:

    o   Hydrography -- This category of data describes combined hydrography
        consisting of all flowing water, standing water, and wetlands.

    o   Transportation -- This category of data includes major transportation
        systems collected in three separate subcategories labeled:  (1) roads
        and trails, (2) railroads, and (3) pipelines, transmission lines, and
        miscellaneous transportation.

   o    Hypsography -- This category of data consists of information on
        topographic relief (primarily contour data), and supplementary spot
        elevations.

   o    Boundaries -- This category of data consists of (1) political boundaries
        that identify States, counties, cities, and other municipalities, and
        (2) administrative boundaries that identify areas such as National and
        State forests.  Political and administrative boundaries are always
        collected as a single data set.

   o    Public Land Survey System (PLSS) -- This category of data describes the
        rectangular system of land surveys that is administered by the U.S.
        Bureau of Land Management.  PLSS data are only collected for areas
        falling solely, or in part, within the States that were formed from the
        public domain.  The PLSS subdivides the public domain and represents
        property boundaries or references to property boundaries.  These DLG
        data are not intended to be official or authoritative.  They are
        presented as cartographic reference information.  The only legal basis
        for determining land boundaries remains the original survey.

The hypsography, boundary, and PLSS categories were authorized for production in
late 1987.  Currently there is very little data available in these categories.

The remaining categories:  manmade features, survey control, vegetative surface
cover, and nonvegetative features are projected to enter the production phase in
1990.


                           DATA STRUCTURE

                        Levels of Structuring

The term Digital Line Graph (DLG) is used by the USGS to describe a digital map
data set in vector form.  Originally, three levels of DLG data (DLG-1, DLG-2,
and DLG-3) were envisioned; these levels were differentiated by their
positional accuracy, level of attribute coding, and relational spatial
information.  It was found, however, that the widest user community would by
served by producing DLG-3 data, which have the full range of attribute codes and
are fully topologically structured.  These two properties are required by users
whose work includes both graphic and analytic applications.  Therefore, all DLG
data in the National Digital Cartographic Data Base are level 3.


                               Topology

Current data collection from 1:100,000-scale maps is exclusively directed toward
producing fully topologically structured level 3 DLG data referred to as DLG-3.
The DLG-3 concept is based on graph theory in which a two-dimensional diagram
is expressed as a set of nodes (topologically significant points), lines, and
areas in a manner that explicitly expresses logical relationships.  Applied to
a map, this concept is used to encode the digital data with the spatial
relationships between map elements which are obvious when the map is examined
visually.  The spatial relationships include such concepts as adjacency and
connectivity between features on the map.  The abstraction of the map data
according to the rules of graph theory preserves the spatial relationships
inherent in the map graphic and creates a logical and consistent data file
structure for computer processing.  A digital file of cartographic or geographic
data that maintains the spatial relationships inherent in the map is called a
topologically structured data file.  A topologically structured data file can
support simple graphic applications, such as plotting streams and roads for base
maps, as well as more advanced applications, such as computations and analyses
involving areas and lines and their spatial relationships.


                        Topological Elements

A DLG-3 file is composed of three separate, but related, elements:  nodes,
lines, and area identifiers.  Nodes define the location of the endpoints of
every line, and a single node may mark the start or end of one or more lines.
Thus, nodes occur at intersections of linear features and other places on linear
features where the feature is subdivided into separate line segments.

A line is an ordered set of points that describes the position and shape of a
linear feature on the map.  Each line starts at a node and ends at a node, and
has an area to the left of its direction of travel, and has an area to the right
of its direction of travel.  The direction of travel is arbitrarily determined
at the time of data capture.  Lines connect to each other at nodes, and a line
does not cross itself or any other line.  A line may describe the boundary
between two areal map features, such as counties, or may define a map feature by
itself, such as a road.  A special line, called a degenerate line, is used to
define features symbolized as independent points on a map.  A degenerate line
starts and ends at the same node, has two identical coordinate pairs, has zero
length, and has the same area to the left and right of the direction of travel;
that is, it is totally enclosed inside one map area.

An area is a portion of the map bounded by lines.  All portions of the map must
be assigned some area point.  Each area is identified in a DLG-3 data file by a
point chosen to represent the characteristics of the area. Newer versions of the
processing software, the DLG Production System or PROSYS, locate a given area
point inside the area it represents, although this is not a structural
requirement.  Every DLG data file will have at least two areas identified:  one
representing the area covered by the file and the other representing the area
outside the coverage of the file.  Additional areas will be identified as
necessary to subdivide the area covered by the file.  Polygons as unique
features are not defined explicitly in a DLG file.  However, polygons can be
constructed using line-area linkages built into the DLG data structure.


                           ATTRIBUTE CODES

In addition to locational and topological information, DLG data elements may
have explicitly encoded attributes.  Attribute codes, also called feature codes
or classification attributes, are used to describe the map information
represented by a node, area, or line. For example, the attribute code for an
area might identify a lake or a swamp; the attribute code for a line might
identify a road, railroad, stream, or shoreline; the attribute code for a node
might identify the upper origin of a stream (fig. 1).  The codes are based on
the cartographic features symbolized on the USGS Topographic Map Series.  These
maps are the basic source material used to digitize and to encode the data
elements and therefore the map symbology has a strong influence on the overall
classification strategy.  A listing of all the attribute codes currently
assigned and used in the 1:100,000- scale DLG files is given in Appendix D.
Detailed information on how to apply and interpret the attribute coding system
is given in Standards for Digital Line Graphs, Part 3:  Attribute Coding.  (This
publication may be purchased from the U.S. Geological Survey.  See the Ordering
Information inside the front cover.)

















    Figure 1.--Map elements showing roads, railroads, buildings,
                 streams and lake and forest areas.


Each attribute code identifies the major category to which a data element
belongs, as well as the specific nature of the element.  Codes also may provide
additional descriptive information.  Most elements are uniquely described by a
single attribute code.  Others, however, may require two or more codes for a
complete description.  If multiple attributes are needed to describe an element,
the order is not usually significant.  Allowing for a variable number of
attribute codes creates an open-ended structure to which information may be
added at any time.  It is not necessary for each element to have associated
attributes; in general, attribute codes are not assigned to an element if the
attributes can be derived based on relationships to adjacent elements.  For
example, the mapped outline of an alkali flat is not assigned an attribute code
because the line record carries a reference to the areas to the left and right.
One area will be assigned an attribute code identifying the area as "alkali
flat" and the other will have no attribute, signifying it is background or
"nonhydrographic."  The fact that the line defines an alkali flat is derivable.

A DLG attribute code is composed of two distinct numeric fields:  a three-digit
major code, which identifies the major category to which the element belongs,
and a four-digit minor code, which specifically describes the element.  In the
digital file, the major and minor attributes are encoded in two integer fields
of six digits, right justified with leading blanks (FORTRAN 2I6 format).  In
this document, major codes are presented as three digits, and minor codes are
presented as four digits.  Leading zeros are shown for clarity; for example:
050  04l2.


                 Major Attribute Codes

A list of the major codes for the categories that are currently being collected
is contained in table 1.  The first two digits of the major code uniquely
identify the category to which the described element belongs.  The third digit
of the major code is used to modify the minor code in two ways:

   o    If zero, the minor code represents a description or classification of
        the element.

   o    If nonzero, the minor code which follows is a parameter requiring
        special interpretation according to instructions given in the codes for
        each category (see next section).


  Table 1.--Major codes used for DLG base categories
















                  Minor Attribute Codes

The first digit of the minor code is normally zero.  If nonzero, it is used as a
modifier to provide additional information such as road access or railroad
status.

The remaining three digits are normally used to indicate the cartographic
interpretation to be applied to specific elements.  The type of element
described by a particular code usually can be determined from the range of value
of the last three digits:

00l - 099 = nodes
l00 - l99 = areas
200 - 299 = lines
300 - 399 = degenerate lines
400 - 499 = codes which may be applied to any element type (nodes,
                lines, areas, or points)
60l - 699 = general descriptive codes

The last three digits (and occasionally all four digits) also may be used as a
parameter code. Parameters are used when a minor code can legitimately assume
a range of values such as a water elevation or a highway route number.  The
meaning of a parameter code is indicated by the (nonzero) third digit of the
major code.


                Sample Attribute Codes

Three examples using the DLG attribute codes follow and should be interpreted
with reference to Appendix D.

Example A:

050  04l2       The major code 050 indicates the combined hydrography category.
                The minor code 04l2 identifies the feature as a stream.

Example B:

170  0201       The major code 170 indicates the roads and trails subcategory in
                the transportation category.  The minor code 0201 identifies the
                feature as a class 1 highway.

l70  0603       The major code l70 indicates the roads and trails subcategory in
                the transportation category.  The minor code identifies the
                feature as a road under construction.  This code would be used
                in addition to the code describing the class of road, and would
                appear in the same record with the code 170 0201.

Example C:

055  0033       The major code 055 indicates a river mile mark for the
                hydrography category.  Because the last digit of the major
                code is nonzero, the minor code is a parameter.  The minor
                code 0033 indicates that the value of the river mile mark at
                that point is 33.

Example D:

306  0033       The major code 306 indicates an Origin of Survey code for
                the U.S. Public Land Survey System category.  Because the
                last digit of the major code is nonzero, the minor code 0033
                indicates that the area element is referenced to the
                Willamette Meridian.


              SAMPLE LINE GRAPH STRUCTURE

Examples of a line graph and its corresponding digital records are given in
figure 2 and table 2.  These examples are simplified representations of the
concepts used in the DLG-3 structure; they are not actual data files.  The
examples shown are composed of 13 nodes, 5 areas, and 15 lines.  The 13 nodes
are labeled N1 through N13, the 5 areas are labeled A1 through A5, and the 15
lines are labeled L1 through L15.  Each element type is maintained as a separate
list in the digital data.

The map represented by the example is divided into five distinct areas labeled
Al through A5.  Area Al represents all the area outside of the map border.
There is one outside area for each DLG-3. It is always the first area
encountered and has the attribute code 000 0000.  In the example given in figure
2, the portion of the map inside the border is divided into four areas, each
bounded (closed) by lines.  Area A2 is bounded by lines Ll4, Ll, L4, and L5.
Area A3 is bounded by lines L3, Ll3, L4, L6, L7, L8, L15, and L9.  Area A4 is
bounded by lines L8, L15, and L9.  Area A5 is bounded by lines L5, L6, L7, and
Ll0 and L2.

As implemented in the standard DLG-3 data structure, line elements contain the
only explicit topological references.  Each line contains pointers to its
bounding nodes (starting and ending) and the areas that it bounds (left and
right of the line).  This format minimizes redundant linkages to achieve
efficient data encoding and storage.

The lines in figure 2 are labeled L1 through L15.  The lines can be identified
by their starting node number, ending node number, number of the area to the
left of the direction of travel, number of the area to the right of the
direction of travel, and string of coordinates describing the alignment of the
line.  In this example, only two pairs of coordinates are shown; however, in
an actual file, an irregular line would have a variable number of coordinate
pairs up to a limit of 3,000 coordinate pairs.  The direction of travel of the
line is arbitrarily determined during the digitizing operation.  In this
example, L1 is encoded as proceeding clockwise around area A2.  Thus line L1
starts at node N1, ends at node N3, has area A1 to the left of the direction of
travel, and has area A2 to the right of the direction of travel.  The coordinate
string





































             Figure 2.--Sample line graph.


describing the alignment of the line will start with the same coordinate values
as that of node N1 and will end with the same coordinate values as that of node
N3.  Because the area to the left of its direction of travel, A1, is different
from the area to the right of its direction of travel, A2, the line is known to
be a boundary between the two areas.

Lines L11 and L12 are examples of lines that lie within one area.  In this
example, line L11 starts at node N5, ends at node N6, has area A5 to the left of
the direction of travel, and again has area A5 to the right of the direction of
travel.  The coordinate string for the line will start with the same coordinate
values as that of node N5 and will end with the same coordinate values as that
of node N6.  Line L12 is an example of a degenerate line.  The line starts at
node N9, ends at node N9, and has area A2 as both the area to its left and
right.  There are only two

                Table 2.--Digital description of sample DLG-3 (see
                          fig. 2)






































coordinate pairs in the string defining the line:  both points have the same
coordinate values as node N9; thus, the two points are the same and the line has
zero length.

The line graph concept allows all of the points on the map to be described as a
member of a line graph element (node, area, or line) with minimal redundancy.
The relationships between the various elements are indicated by the structure.
Note that in this example the x and y coordinates are numbered from the lower
left corner to simplify the drawing.  In an actual DLG-3 file, the origin is the
center of the map and the internal file coordinates are numbered plus or minus 1
to 32,767 in thousandths of inches.  See the section labeled "coordinate
systems" for more detail.


                GRAPH THEORY IN DLG DATA

The digital line graph concept is based on graph theory, in which a diagram
can be expressed as a set of elements (nodes, areas, and lines) in a manner that
shows logical spatial relationships with minimal redundancy. There are three
ways to implement the line graph concept in DLG files: the area case, the
network case, and the area-hybrid case.  These cases are differentiated by the
nature of the information contained in the category.  Currently all NMD files
are processed as area-hybrid case DLG's.


                       Area Case

Area line graphs can be used to represent area features such as political
entities or the U.S. Public Land Survey System.  In the pure area case, each
line element bounds two different area elements, all closed circuits of lines
form unique areas, and all areas are attribute coded.  Line elements for area
line graphs are not usually assigned primary attributes. The primary attribute
characteristics of lines in these categories are derived by examining the
attributes of the area elements on either side of the lines.


                     Network Case

Network line graphs can be used to represent linear features such as roads,
railroads, or pipelines.  The major topological relationship expressed by
network data is that of connectivity.  The network case differs from the area
case in that, irrespective of the number of closed areas forming the graph, only
two areas are encoded:  (1) the area outside the graph, termed the outside
area; and (2) the area within the graph, termed the background area.  All lines
except the graph boundary, or neatline, are considered to be contained within
the background area. Lines may exist within the background area that are not
part of closed line circuits.  In the pure network case, the lines themselves
have the identity and carry the appropriate attribute codes.  Data encoded in
network line graph form are suitable for various forms of network analysis,
such as minimum path computations.


                   Area-Hybrid Case

In the area-hybrid case, network and area type information are gathered in a
single DLG file.  In this approach, all closed circuits of lines define unique
areas.  The unique areas which represent features for the overlay are given
attribute codes.  The remaining areas are recognized in processing as individual
unattributed background areas.  Linear features may exist which do not form
boundaries between two areas.  These lines may occupy a position in an
unattributed background area, or in an attributed area.  Lines that have
significance in themselves are assigned attribute codes.  For example, in the
hydrography overlay, areal features such as lakes and swamps will be encoded
with the appropriate attributes; surrounding nonhydrographic areas will be
uncoded.  Linear features such as streams and aqueducts receive the appropriate
line code; unattributed lines may also exist (e.g. around defined areal features
such as an alkali flat).

Figure 3 shows a 7.5-minute window taken from the Cartersville, Ga.,
1:100,000-scale quadrangle.  Figure 4 shows the line graph encoded for the
hydrography of the same area.  Certain nodes, areas, and lines are labeled.









































Figure 3.--Window from the Cartersville, Ga., 1:100,000-scale USGS
                    quadrangle map.














































Figure 4.--Plot from line graph of hydrography, Cartersville, Ga.,
7.5-minute section of quadrangle, with enlarged detail.

Table 3 contains some of the digital data records, extracted from the standard
format DLG file, which describe this portion of the graph.  The internal
sequence identification numbers shown reflect the order of these features in the
original file.  (Note:  Descriptions of DLG-3 formats are contained in
Appendixes A and B, and a list of attribute codes is contained in Appendix D.)

Table 3.--Selected sample of standard format DLG-3 records of Cartersville,
Ga., 7.5-minute section of quadrangle


















































Table 3.--Selected sample of standard format DLG-3 records of
Cartersville, Ga., 7.5-minute section of quadrangle--continued

Table 3.--Selected sample of standard format DLG-3 records of
Cartersville, Ga., 7.5-minute section of quadrangle--continued


























In the Cartersville example, each node and area element is described by one or
two logical records:  (1) a type D.l record that describes the element, and (2)
an optional type F record that lists the attribute codes associated with the
element.  The first record (type D.1) for each node and area element contains
the following fields:

1.Type of record indicator, N for node or A for area.
2.Internal sequenceidentification number.
3.X-coordinate of node or representative area point.
4.Y-coordinate of node or representative area point.
5.Number of attribute codesthat describe the element.
6.Number of pairs of characters in the text string that describes the element.

The second record (type F) for each node and area element contains n attribute
codes (expressed as major and minor code pairs), where n is the number specified
in field 5 of the first (type D.l) record.

Each line element in the Cartersville example is described by two or three
logical records:  (1) a type D.2 line description record, and (2) a type E
record that lists the x,y coordinate pairs that define the shape of the line,
and, if appropriate, (3) a type F (attribute code) record.  The first record
(type D.2) for each line element contains the following fields:

1.Type of record indicator (L).
2.Internal sequence identification number.
3.Internal sequence number of starting node.
4.Internal sequence number of ending node.
5.Internal sequence number of the area to the left of the line. 
6.Internal sequence number of the area to the right of the line. 
7.Number of x,y coordinate pairs that locate the line on the map.
8.Number of attribute codes that describe the line.
9.Number of pairs of characters in the text string that describes
the line.

The second logical record (type E) for each line element contains n coordinate
pairs, where n is the number specified in field 7 of the first (type D.2)
record.  The type F record is as described above.

The specific records listed in table 3 completely describe several hydrographic
features in the upper left section of figure 3, the Oostanaula River, a small
irregularly shaped lake, and the single line stream flowing from the lake to the
river.  The records referred to in the following description have been extracted
from a complete DLG.  Therefore the internal sequence identifiers reflect the
original order of the features in the file.  The records are referred to by the
internal sequence number, e.g., area 4, node 77, line 82.

The double line stream, Oostanaula River, is represented by area record 5 and
identified by the attribute code 050 0412.  Area records 4 and 6 are the
background areas on either side of the river and as such have no attribute
code assigned.  The area outside of the map is represented by area record 1 and
is identified by the attribute code 0 0.

Line records 55, 58, 66, and 72 form the left bank of the river, coded as though
one were facing downstream.  They are identified by the attribute code 050 0606.
They can be chained by referring to the nodes.  Line record 72 starts at node 8
and ends at node 6.  Line record 66 starts at node 6 and ends at node 77.  Line
record 58 starts at node 77 and ends at node 73.  Line record 55 starts at node
73 and ends at node 72.

The right bank of the river is formed in a similar fashion by line records 69
and 70, which are identified by the attribute code 050 0605.  They are similarly
linked through the nodes 7, 80, and 74.  Note that the identity of the shoreline
as either left or right bank, (coded as such to indicate downstream flow), is
established by the attribute code without changing the identity of the feature.
The given line segments making up the shore may be digitized in either
direction.  The segment of neatline represented by line record 68 stretches from
node 7 to node 74, the two places where the right bank intersects the neatline.
The neatline has no attribute code assigned but can be identified by the fact
that the area on one side of it is the outside area, area 1.

Area record 8 is the irregularly shaped lake.  It is identified by attribute
code 050.0421.  Its shoreline is formed by line records 80, 81, and 82, which
are identified by attribute code 050.0200.  These lines also can be identified
as bounding area 8, by reference within the line record to area 8 being located
either to the left or right of the line (depending on which way the digitizer
traced each line).  The lines can be chained by referring to the starting and
ending nodes 90, 15, and 88.

The single-line stream that flows from the lake to the Oostanaula River is
represented by line records 6 and 7 and identified by attribute code 050.0412.
One stream segment connects to the lake at node 15 and one to the left river
bank at node 6.  The segments of the stream are themselves linked at node 11.
Note that this stream has the same attribute code as the river.  This is because
both are streams, one of which is digitized as a line and one of which is
digitized as an area and its delimiting banks.  The direction of flow of this
stream can be derived from the fact that node 15 is identified with attribute
code 050.0005 (stream exiting hydrographic area).  Background area 4 is located
on both sides of the stream.


                 DISTRIBUTION FORMATS

The 1:100,000-scale DLG data are available in two distribution formats: (1)
standard and (2) optional.

The standard distribution format is intended to minimize storage requirements.
Explicit topological linkages are contained only in the line elements (starting
node, ending node, area to the left of direction of travel, area to the right of
direction of travel).  A sample DLG in standard format is found in Appendix A.

The optional distribution format was designed to facilitate data usage. The
topological relationships explicitly encoded include starting node, ending node,
area to the left of direction of travel and area to the right of direction of
travel for line elements, bounding lines for area elements, and bounding lines
for node elements.  These files are typically larger than those in the standard
format but, for certain applications, can simplify processing requirements.  For
example, topological linkages are explicitly encoded for all line, node, and
area elements, allowing a polygon data structure to be easily created.  These
linkages facilitate GIS applications of DLG data as well as generation of
graphic products. A sample DLG in optional format is found in Appendix B.

The characteristics of the standard and optional DLG formats are summarized
below in table 4.


                   SOURCE MATERIALS

The DLG data files described in this document are derived from USGS topographic
maps published as 30- x 60-minute quadrangles at 1:100,000- scale.  Where
1:100,000-scale coverage is not available, the following sources are used, in
order of preference:

1.Bureau of Land Management editions of 1:100,000-scale maps,
2.Archival compilation materials, if available.

       Table 4.--Standard and optional DLG format



















The scale of the source materials used to generate a DLG is contained in the
file header.  The scale is also reflected in the resolution field, which states
the ground length in meters of the smallest data collection unit 0.001 inch
(2.54 m).


               CELL SIZE AND FILE EXTENT

The DLG's are distributed in groups of files that make up a 30- x 30minute area
of coverage representing the selected category of information in the east half
or west half of a 1:100,000-scale source map.  Each 30-minute area consists of a
varying number of DLG files depending on the category and the feature density.
The normal distribution group will be four 15-minute files per 30-minute area.
If the feature density in an area is such that the file size would exceed the
limitations of the processing programs, then that 30-minute area will be covered
by sixteen 7.5-minute files.  This seldom occurs except in the case of roads and
trails in large cities.

For the categories currently available, the 30-minute area of coverage will
comprise the following:

 Category
 Number of files
 Size

 Hydrography Normal     4
15 minute Very Dense    167.5 minute

Transportation
  Normal
    Roads and trails     4 15 minute
    Railroads     4 15 minute
    Pipelines, Transmission     4 15 minute
      Lines and Miscellaneous
      Transportation
  Very Dense
    Roads and trails    167.5 minute
    Railroads     4 15 minute
    Pipelines, etc.     4 15 minute

Hypsography
  Normal     4 15 minute
  Very dense    167.5 minute

Boundary*
  Normal     4 15 minute

PLSS*
  Normal     4 15 minute

*Boundary and PLSS overlays are by nature less dense and will always be
 contained within four 15-minute files.

                                                                 


The quadrangle name field in the header record will contain the name of the
1:100,000-scale source map.  However, the pieces or sections into which each is
divided are identified within the header (A) record to the size and placement of
each.  In column 64-66, each section will be identified by a 3-character code
XNN where:

X is a single letter indicating size
F = Fifteen (15) minute block
S = Seven and a half (7.5) minute block

NN is a two-digit number indicating the specific quad.  Figure 5 illustrates
this division with the sections labeled with the code that would appear in
column 64-66 of the header record.

If data for a particular category exist only in a portion of a 30-minute area,
the entire area will be digitized.  The 7.5- or 15-minute sections which contain
no feature in the given category will be digitized as "null" or empty files.
This means they will contain the neatline records, inside















    Figure 5.--Sectioning scheme for DLG data of a
              1:100,000-scale quadrangle.

area record, and outside area records only in order to indicate the absence of
any features in that category in that location.  The remaining 7.5- or 15-minute
sections which contain features in that category will be digitized as usual.

If no data for a particular category exist in an entire 30-minute area the
entire 30-minute area will not be digitized.  This occurs on coastal areas where
an entire 30-minute area may be ocean, or along the national boundary where an
entire 30-minute area may lie outside the United States. Data are not currently
collected in Canada or Mexico.  At some time in the future, the non-U.S. areas
will be digitized and added to the NDCDB.

Nonstandard cells are not collected.  In areas where map format is sometimes
extended to conform to the shoreline or national boundary, the portion of the
map that extends beyond the normal size is digitized as a separate file.  Such
cells are readily identified by examining the geographic coordinate limits
contained in the file header.  Such files may also be identified by the name
which will be formed by adding descriptive information to the map name, such as
"Mt. Baker O.E. N" (Mt. Baker over-edge North).


                   Preliminary Data

In mid-1986, the U.S. Geological Survey released a preliminary version of DLG's
from 1:100,000-scale maps.  These data differ in format from those previously
described.  Specific characteristics of these preliminary data are given below.

1.These data are topologically structured, attribute coded, and will be
distributed in standard or optional DLG format.

2.The DLG's are distributed in groups of files that make up a 30by 30-minute
area of coverage representing a category of information in the east half or
west half of a 1:100,000-scale source map.  The distribution groups for both
roads and trails, and hydrography will consist of sixteen 7.5-minute files
(rather than four 15-minute files).

3.Railroad and miscellaneous transportation data consisting of a single
30-minute file will contain a 3-character TNN code in columns 64-66 of the
header (A) record where: T = Thirty-minute (30) block NN = A two-digit number
indicating the West (01) or East (02) half of a 1:100,000-scale graphic.

4.Preliminary data have not been processed through edge-matching software and
will not include edge-join quality control flags.

The USGS is currently involved in a program to reformat data, originally
available for distribution in preliminary format, to standard cell size. Data
that have been processed through edge-matching software and reformatted to the
standard cell size automatically supercede preliminary format data.


                  COORDINATE SYSTEMS

The positional descriptions for DLG data elements are expressed in one of two
coordinate systems, dependent upon the distribution format selected. These are
described as follows as the standard distribution format and the optional
distribution format.


             Standard Distribution Format

The DLG data in the standard distribution format are encoded using an internal
file coordinate system to minimize storage requirements.  The characteristics of
this system are as follows:

1.The coordinate system is Cartesian.
2.The origin (x=0, y=0) is at the center of the cell.
3.The x-axis of the coordinate system is parallel to a theoretical
straight line connecting the southwest and southeast corners of
the cell, y-axis is perpendicular to that line.
4.One unit is equal to 0.00l-inch at map scale.
5.The coordinate domain is limited to the range -32767 to +32767.

The file header contains the parameters of a transformation which can be used to
convert the internal file coordinates to the ground coordinate system, which is
the Universal Transverse Mercator (UTM) for 1:100,000scale DLG's.  An example of
this transformation is given in Appendix E.


             Optional Distribution Format

The DLG data in the optional distribution format are expressed in the units of
the ground coordinate system, that is, meters in the UTM coordinate system.

                    DATA VALIDATION

The DLG data do not currently carry quantified accuracy statements.  The
following procedures, however, are used to validate the data files before they
are released for distribution:

1.File fidelity and completeness -- The data are either manually digitized using
equipment with a resolution of 0.00l inch and an absolute accuracy of from 0.003
to 0.005 inch, or are scanned on an automatic device with a resolution of 30
points per millimeter, or 0.0013 inch.  The positional accuracy of the data and
completeness of the file are checked by visually comparing proof plots with the
original stable-base source material. These proof plots are generated using
automated drafting machines with a resolution of 0.00l inch and an absolute
accuracy of from 0.003 to 0.005 inch.

2.Attribute accuracy -- DLG attribute codes are checked by software against a
table of valid codes to ensure that each attribute in a file is valid for the
category and element type to which it is assigned.  Validating the codes for
correct application is currently a manual process involving the correlation of
formatted listings with proof plots and graphic displays.

3.Topological fidelity -- The topological structure of each DLG file is fully
validated by software.  There are no extraneous intersections; that is, a line
does not join or cross another line, or itself, except at a node.  No line
extends through a node.  Polygon (area) adjacency is also validated; that is,
area left and right topological attributes of lines are consistent throughout
the file. The neatline is free of gaps.  Validation of DLG data is performed for
each category within a file.

Additional data validation is being implemented as follows:

1.Edge matching -- Validation software provides for checking the edges of each
quadrangle against the edges of the four adjacent quadrangles.  Each edge of a
DLG-3 is checked for positional and attribute matching along the neatlines of
the adjoining DLG-3 cells, providing that the surrounding data cells are
available at the time the DLG-3 is entered into the NDCDB.  There is currently
no attempt, other than the coding of coincident features, to provide fully
integrated data categories.

2.Quality Control Flags -- Information in the header of the DLG-3 indicates the
status of the file with respect to the edge matching described above.  Twelve
bytes at the end of record A.1 in the standard distribution format and at the
end of record 3 in the optional distribution format of the ASCII file are set
aside for quality control flags (see Appendices A and B).  The first three of
these flag positions are for future use.  The fourth flag position contains a
value encoded in the bit pattern that is used only by the data base manager to
check the edge status.  The remaining eight flags indicate to the user the edge
status code and the status reason code.  The four status flags contain the
status of the West, North, East, and South edges of a DLG-3 as compared to the
edges of the four adjoining DLG-3 files.  Each of the four flags is followed by
a status reason code that explains the status of the four edges respectively.

The possible status values for a DLG-3 entered into the NDCDB are:

(blank) = unchecked
0 = passed edge match check
1 = alignment discontinuity
2 = attribute discontinuity
3 = attribute and alignment discontinuity

The possible reason flags are: 

(blank) = no reason code set ("unchecked" for some earlier data sets)
4 = adjacent data do not exist
5 = adjacent data unavailable
6 = graphic discontinuity
7 = mismatch valid
8 = paneling unauthorized

The following combinations of status flags and reason flags are currently valid
for the processing software.

blank,blankblank,4blank,5blank,8
0,blank
1,6   1,7
2,6   2,7
3,6   3,7

The following is a brief explanation of the reason flags.

4 = adjacent data do not exist -- This flag is used with a status flag of blank
(unchecked).  This combination exists primarily for file edges which are
adjacent to areas unmapped within the series/scale of products being digitized,
e.g. coastal and international boundary locations.  These flags are also used
for Public Land Survey System (PLSS) file edges which border areas of the
country not having PLSS information.

5 = adjacent data unavailable -- This flag is used with a status flag of blank
(unchecked).  This flag is appropriate for edges adjacent to areas having
similar source material and data categories, but which have not been digitized
and archived.  A reason code with the value of 5 may be reset as the adjoining
data cell becomes available for edge match verification.

6 = graphic discontinuity -- This flag indicates a discontinuity in
classification or alignment between features on adjacent graphics which were
digitized as represented.

7 = mismatch valid -- This reason flag applies in the case of a linear graph
element ending precisely on the neatline or having a reasonable attribute value
change as it crosses the neatline, (e.g. a single line stream ending on the
neatline, a road changing from third to fourth class at the neatline).

8 = panelling unauthorized -- This flag is used with the edge status flag of
blank and indicates that no authorization was in place for edge matching at the
time the data were archived.

This flag is to be used when adjoining quads do not match in cell size (e.g. the
situation internal to a 1:100,000-scale project, where a standard 15-minute
distribution file adjoins four 7.5-minute files, which cannot at this time be
merged into standard 15-minute format because of the density of the data).

In the course of checking and aligning an edge, it is possible to encounter
more than one reason for a mismatch status, such as both valid and graphic
discontinuities.  In such cases the reason flag is to be set to indicate the
"worst case," i.e. the reason indicating the most serious problem with the edge
and which in most cases would require some degree of correction in the future.
For the above example, the graphic dis- continuity reason flag would be set in
preference to the mismatch valid flag.

When an edge status code is other than "0", the DLG-3 file will be entered into
the DCDB only when the reason code has also been set as a result of examination
of the file.























                      APPENDIXES

      APPENDIX A.--Standard DLG Distribution Format
                   (Record Contents)

In the standard DLG format, the topological linkages are contained only in the
line elements.  The files are physically comprised of standard ASCII characters
organized into fixed-length logical records of l44 characters.  Nine distinct
record types are defined.

Logical 
record 
type                 Content

A            Header record containing DLG
               identification information.
B            Header record containing projection
               information and registration points.
C            Header record identifying data categories
               contained in this DLG and indicating the
               number of nodes, areas, and lines in each
               category.
D.l          A node or an area record.
D.2          A line record.
E            Record containing x,y coordinate strings.
F            Record containing attribute codes.
G            Record containing text string (not currently used).
H            Accuracy estimate (not currently used).

      APPENDIX A.--Standard DLG Distribution Format
             (Record Contents)--continued


The actual sequence of records in a standard distribution DLG file is as
follows:

l.  Header records
      Type A (one record)
      Type B (one record)
      Type C (one record)

2.  Data records                    
      Node records                  Repeated
        Node description (D.l)      for each
        Attribute codes (F)         node within a
        Text string (G)             data category

      Area records                  
        Area description (D.l)      Repeated
        Attribute codes (F)         for each
        Text string (G)             area within a
                                    data category

      Line records                  
        Line description (D.2)      Repeated
        X,Y coordinates (E)         for each
        Attribute codes (F)         line within a
        Text string (G)             data category

3.  Accuracy estimate
      Type H (one record) (not currently used)

Descriptions of the contents of records A-F are contained in the following
tables.  The tables also reflect the relationship between these record types and
l44-byte logical records.



                 APPENDIX B.--Optional DLG Distribution Format
                   (Record Contents)

In the optional DLG distribution format, topological linkages can be explicitly
encoded for node and area elements as well as for line elements.  The files are
physically comprised of ASCII characters organized into fixed-length logical
records of 80 characters (bytes). Bytes 1-72 of each record contain DLG data,
and bytes 73-80 may be blank or contain a record sequence number.

The record types used in the optional DLG distribution format may be categorized
as header and data records.

The following are considered header records:

   o    File identification and description records (variable record formats)
   o    Accuracy/miscellaneous records (not currently used)
   o    Control-point identification records oData-category identification
        records

The following are considered data records:

   o    Node and area identification records
   o    Node-to-area linkage records*
   o    Node-to-line linkage records
   o    Area-to-line linkage records
   o    Area-to-node linkage records*
   o    Line identification records
   o    Coordinate string records (lines)
   o    Coordinate string records (areas)*
   o    Attribute code records
   o    Text records (not currently used)

*Data distributed in optional format from the NDCDB will not contain these data
records.

APPENDIX B.--Optional DLG Distribution Format (Record Contents)--continued

The actual sequence of records in an optional distribution format DLG file is as
follows:

l.  Header records
      Ten file identification and
        description records
      Accuracy records (not currently used)
      Control point identification records
        (one per control-point)
      Data category identification records
        (one per data category in the file)

2.  Data records                               
      Node identification record               
        Node-to-area linkage record(s)*        Repeated
        Node-to-line linkage record(s)         for each
        Attribute code record(s)               node within a
        Text record(s)                         data category

      Area identification record               
        Area-to-node linkage record(s)*        Repeated
        Area-to-line linkage record(s)         for each
        Coordinate string record(s)*           area within a 
        Attribute code record(s)               data category
        Text record(s)

      Line identification record               Repeated
        Coordinate string record(s)            for each
        Attribute code record(s)               line within a
        Text record(s)                         data category

*Data distributed in optional format from the NDCDB will not contain these
records.

Descriptions of the contents of the various types of records in an optional
distribution format DLG are contained in the following tables.

                         APPENDIX C.--Map Projection Parameters
                                      Universal Transverse Mercator (UTM)

The standard and optional DLG distribution formats include 15 fields reserved
for map projection parameters.  These parameters are typically used as input for
a coordinate transformation package such as the USGS General Cartographic
Transformation Package (GCTP).

When the ground coordinate system of a DLG is the Universal Transverse Mercator
system, as in the case for all DLG's digitized from 1:100,000scale maps, only
the first two of the 15 parameter fields are used:

1.Longitude of any point in UTM zone.       Normally placed at the
2.Latitude of any point in UTM zone.        center of the DLG cell.

3-15.Not used (=0).                                

A transformation to or from UTM using GCTP can be controlled by specifying the
UTM zone or by supplying the geographic coordinate in parameters 1 and 2, from
which the UTM zone is computed by GCTP.  In a DLG file, the parameters are
encoded as packed, degrees-minutes-seconds (DMS) as follows:

degrees * 1000000 + minutes * 1000 + seconds

Example:  If degrees = +50, minutes = 30, and seconds = 36.25, then the
parameter value is 50030036.25 stored as a REAL*8 variable, and
"bb0.500300362500000D 08" encoded in FORTRAN D24.15 format.

         APPENDIX C.--Map Projection Parameters
    Universal Transverse Mercator (UTM)--continued

            Codes for UTM Coordinate Zones

West Longitude (degrees)                            Zone

l80-l74                                           l
l74-l68                                           2
l68-l62                                           3
l62-l56                                           4
l56-l50                                           5
l50-l44                                           6
l44-l38                                           7
l38-l32                                           8
l32-l26                                           9
l26-l20                                           l0
l20-ll4                                           ll
ll4-l08                                           l2
l08-l02                                           l3
l02- 96                                           l4
 96- 90                                           l5
 90- 84                                           l6
 84- 78                                           l7
 78- 72                                           l8
 72- 66                                           l9
 66- 60                                           20

            APPENDIX D.--DLG Attribute Codes




Valid Minor Codes for the Coincident Feature Parameter

Code         Base Category

0002         Hypsography

0005         Hydrography

0007         Surface Cover

0009         Boundary

0015         Survey Control

             Transportation Systems

0017         Roads and Trails

0018         Railroads

0019         Pipelines, Transmission Lines, Miscellaneous
                        Transportation

0020         Manmade Features

                     APPENDIX E.--Coordinate Conversion

This appendix illustrates the procedure for converting the internal file
coordinates of the standard DLG format to the ground planimetric UTM reference
coordinates.  The formulas for this conversion, representing a simple offset,
rotation, and scale, are as follows:

            X = Alx + A2y + A3, and
            Y = Aly - A2x + A4,

where X and Y are the ground planimetric coordinate values and x and y are the
internal file coordinates.

The parameters for these formulas (Al, A2, A3, and A4) are contained in Header
Record B, as double-precision floating-point numbers.

This example converts four coordinate pairs from internal file coordinates to
ground planimetric UTM zone l0 coordinate values.  The parameters are as
follows:

           Al =.60959440759
           A2 = -.00288l7856942
           A3 = 538248.7934l
           A4 = 4240374.4556

The internal file coordinates to be converted are as follows:

                        x                   y

           lst pair  -897l               -ll376
           2nd pair  -8955                ll375
           3rd pair   8955                ll376
           4th pair   897l               -ll376

The calculations to determine the ground planimetric coordinates for the first
pair are as follows:

           X = (0.60959440759) (-897l) + (-0.00288l7856942) (-ll376)
               +(538248.7934l)   
             =5328l2.9l

           Y = (0.60959440759) (-ll376) - (-0.00288l7856942) (-897l)
               +(4240374.4556)
             =42334l3.86

The resulting X,Y coordinate values for the four pairs are as follows:

                        X                      Y

           lst pair  532,8l2.9l          4,233,4l3.86
           2nd pair  532,757.l0          4,247,282.79
           3rd pair  543,674.93          4,247,335.0l
           4th pair  543,750.25          4,233,465.56
             APPENDIX F.--Sample DLG Data File
              (Standard Distribution Format)


CARTERSVILLE                 GA          1981,        100000.  S01
RO4.HYS01
    3     1    16  -0.840560150000038D+08   0.340260150000010D+08   0.0
                    0.0                     0.0
  0.0                     0.0                     0.0
  0.0                     0.0                     0.0
  0.0                     0.0                     0.0
  0.0                       2    0.254000000000000D+01    0     4
 -0.850000000000000D+02   0.343750000000000D+02  -0.850000000000000D+02
  0.345000000000000D+02  -0.848750000000000D+02   0.345000000000000D+02
 -0.848750000000000D+02   0.343750000000000D+02

  0.253948017060000D+01  -0.516359320290000D-01   0.689504506100000D+06
  0.381240214830000D+07     4
SW -2263 -2729NW -2260  2729NE  2259  2729SE  2263 -2729

     1

HYDROGRAPHY            795   118   795    22   530   138

N      1  2202  2571     1     0

    50     1

N      2   855  2522     1     0

    50     1

N      3  1003  2390     1     0

    50     1

N      4  1626  2381     0     0

N      5  -256  1394     0     0

N      6 -2034  1365     1     0

N      7 -2260  1285     0     0

N      8 -2261  1263     0     0

N      9  -151  1156     0     0

N     10   772  1079     1     0

    50     2

              APPENDIX F.--Sample DLG Data File
         (Standard Distribution Format)--continued


N     11 -1698  1059     0     0

N     12  1912  1028     1     0

    50     1

N     13  -828  1011     1     0

    50     1

N     14  -932   957     1     0

    50     1

N     15 -1292   929     1     0

    50     5

N     16 -2139   922     1     0

    50     1

N     17   489   919     1     0

    50     2

N     18  2162   697     1     0

    50     1

N     19 -1724   212     1     0

    50     2
 
 A      1     0     0     1     0
 
      0     0
 
 A      2     0     0     0     0
 
 A      3  1533  2471     1     0
 
     50   106
 
 A      4     0     0     0     0
 
 A      5 -2057  1523     1     0
 
     50   412
 
              APPENDIX F.--Sample DLG Data File
         (Standard Distribution Format)--continued


 A      6     0     0     0     0
 
 A      7   797  1119     1     0
 
     50   421
 
 A      8 -1243   770     1     0
 
     50   421
 
 A      9   530   916     1     0
 
     50   421
 
 A     10 -1711   129     1     0
 
     50   421
 
 A     11     0     0     0     0
 
 A     12 -1726 -1658     1     0
 
     50   421
 
 A     13     0     0     0     0
 
     50   106
 
 A     17  1365  2584     1     0
 
     50   106
 
 A     18     0     0     0     0
 
 A     19   841  1803     1     0
 
     50   421
 
 A     20     0     0     0     0
 
 A     21   819  -440     1     0
 
     50   421
 
 A     22     0     0     0     0
 
              APPENDIX F.--Sample DLG Data File
         (Standard Distribution Format)--continued


 L      1    74    72     1     5     2     0     0
 
  -2259  1824 -2260  1855
 
 L      2     8     7     1     5     2     0     0
 
  -2261  1263 -2260  1285
 
 L      3     9     5     4     2    13     1     0
 
   -151  1156  -147  1180  -153  1189  -161  1193  -198  1181  -211  1184
   -253  1174  -263  1181  -268  1192  -264  1238  -264  1333  -250  1361
   -256  1394
 
     50   412
 
 L      4   115     8     1     4     2     0     0
 
  -2260  1091 -2261  1263
 
 L      5    10    10     2     7    10     1     0
 
    772  1079   773  1109   794  1161   803  1169   816  1169   823  1162
    824  1117   814  1081   810  1077   772  1079
     50   200
 
 L      6    11     6     4     4    21     1     0
 
  -1698  1059 -1699  1115 -1686  1140 -1686  1178 -1698  1193 -1718  1203
  -1777  1216 -1792  1238 -1838  1257 -1902  1243 -1910  1236 -1911  1212
  -1920  1208 -1929  1214 -1957  1249 -1957  1253 -1981  1281 -2010  1333
  -2009  1351 -2014  1361 -2034  1365
     50   412
 
 L      7    15    11     4     4    17     1     0
 
  -1292   929 -1295   951 -1306   973 -1308   987 -1321  1000 -1359  1019
  -1416  1017 -1430  1008 -1434  1000 -1455   981 -1469   988 -1482  1000
  -1524   994 -1576  1002 -1644  1034 -1669  1050 -1698  1059
 
     50   412
 
 L      8    16   115     4     4    11     2     0
 
  -2139   922 -2154   961 -2160   970 -2167   989 -2179  1006 -2182  1017
  -2206  1041 -2207  1052 -2217  1065 -2250  1079 -2260  1091
     50   412    50   610
 
              APPENDIX F.--Sample DLG Data File
         (Standard Distribution Format)--continued


 L      9    84     9     2     2    29     1     0
 
    444   923   413   928   370   922   360   904   321   886   267   921
    255   934   251   943   235   956   145   952   133   949    94   962
     71   955    44   957    12   981   -26   988   -37   997   -54  1027
    -74  1048   -80  1060   -87  1086   -85  1115   -94  1124   -96  1165
   -110  1179  -127  1175  -131  1158  -144  1153  -151  1156
 
     50   412
 
 L     10    17    17     9     2    12     1     0
 
    489   919   489   908   498   900   510   900   524   906   570   902
    578   910   578   927   529   933   498   932   492   927   489   919
     50   200
 
 L     11    17    84     2     2     3     2     0
 
    489   919   465   924   444   923
 
     50   412    50   610
 
 L     12    87    84     2     2     3     1     0
 
    511   836   472   873   444   923
 
     50   412
 
 L     13    89    87     2     2     3     1     0
 
    527   788   511   816   511   836
 
     50   412
 
 L     14    21    20     2     1     2     0     0
 
   2262   172  2261   200
 
 L     24    49    50    15     1     2     0     0
 
  -1188  2729 -1249  2729
 
 L     25    51    49    14     1     2     0     0
 
  -1146  2729 -1188  2729
 
            APPENDIX G.--Sample DLG Data File
            (Optional Distribution Format)



CARTERSVILLE, GA 01                      1981,        100000.  S01
RO4.RDS01
     3     1    16     2 0.25400000000D+01     4     0     4     1
  -0.840560150000038D+08   0.340260150000010D+08   0.000000000000000D+00
   0.000000000000000D+00   0.000000000000000D+00   0.000000000000000D+00
   0.000000000000000D+00   0.000000000000000D+00   0.000000000000000D+00
   0.000000000000000D+00   0.000000000000000D+00   0.000000000000000D+00
   0.000000000000000D+00   0.000000000000000D+00   0.000000000000000D+00
 0.10000000000D+01 0.00000000000D+00 0.00000000000D+00 0.00000000000D+00
SW       34.375000  -85.000000         683898.58  3805355.05
NW       34.500000  -85.000000         683624.37  3819215.69
NE       34.500000  -84.875000         695100.28  3819449.04
SE       34.375000  -84.875000         695392.26  3805588.76
ROADS AND TRAILS       0   551   551 010   198   198 011   747   747   1
N    1   695392.26  3805588.76           2           0     0
  -724   725
N    2   685742.29  3819258.76           3           0     0
     1    -2   -87
N    3   684845.86  3819240.53           3           0     0
    -1   -23  -258
N    4   687098.38  3819286.33           3           0     0
     2    -3   -34
N    5   687347.30  3819288.85           3           0     0
     3    -4   -35
N    6   687509.77  3819294.70           3           0     0
     4    -5   -42
N    7   687735.78  3819299.29           3           0     0
     5    -6   -43
N    8   687842.44  3819301.46           3           0     0
     6    -7   -45
N    9   687969.42  3819304.04           3           0     0
     7    -8   -67
N   10   688042.96  3819310.62           3           0     0
     8    -9   -66
N   11   688129.40  3819307.29           3           0     0
     9   -10   -80
N   12   688462.08  3819314.06           3           0     0
    10   -11   -31
N   13   688632.22  3819317.52           3           0     0
    11   -12   -32
N   14   688837.92  3819321.70           3           0     0
    12   -13   -24
N   15   688947.12  3819323.92           3           0     0
    13   -14   -26
N   16   689490.57  3819334.97           3           0     0
    14   -15  -154
              APPENDIX G.--Sample DLG Data File
         (Optional Distribution Format)--continued


A    1   689504.51  3812402.15          61    65     1     0     0
  -695  -701  -705  -706  -708  -710  -713  -714  -716  -718  -719  -722
  -723   724   725   693   692   645   576   554   553   545   536   512
   483   407   244   218   146   113    94    21    20    19    18    17
    16    15    14    13    12    11    10     9     8     7     6     5
     4     3     2     1  -258  -399  -464  -509  -543  -547  -557  -620
  -689
     0     0
A    2   689504.51  3812402.15           3     4     0     0     0
   726  -725  -724
A    3   689504.51  3812402.15          10    32     0     0     0
    87    -2   -34   -40    41   -49   -48   -74  -105   104
A    4   689504.51  3812402.15           8    25     0     0     0
   136    23    -1   -87  -137  -139  -141   140
A    5   689504.51  3812402.15           5    28     0     0     0
  -259   258   -23  -136  -237
A    6   689504.51  3812402.15           3     8     0     0     0
    34    -3   -35
A    7   689504.51  3812402.15           5     9     0     0     0
    59    35    -4   -42   -58
A    8   689504.51  3812402.15           4     6     0     0     0
    42    -5   -43    44
A    9   689504.51  3812402.15           4     5     0     0     0
    43    -6   -45    46
A   10   689504.51  3812402.15           4     8     0     0     0
    45    -7   -67    70
A   11   689504.51  3812402.15           4     6     0     0     0
    67    -8   -66   -68
A   12   689504.51  3812402.15           5     6     0     0     0
    66    -9   -80    79    78
A   13   689504.51  3812402.15          17    34     0     0     1
   106   -79    80   -10   -31   -37  -111  -110  -115  -117  -119  -121
   122     0    84    85   -83
A   14   689504.51  3812402.15           3     8     0     0     0
    31   -11   -32
A   15   689504.51  3812402.15           5     9     0     0     0
    39    32   -12   -24   -38
A   16   689504.51  3812402.15           4     6     0     0     0
    24   -13   -26    25
L    1     2     3     4     1                 2     0     0
   685742.29  3819258.76   684845.86  3819240.53
L    2     4     2     3     1                 2     0     0
   687098.38  3819286.33   685742.29  3819258.76
L    3     5     4     6     1                 2     0     0
   687347.30  3819288.85   687098.38  3819286.33
L    4     6     5     7     1                 2     0     0
   687509.77  3819294.70   687347.30  3819288.85
L    5     7     6     8     1                 2     0     0
   687735.78  3819299.29   687509.77  3819294.70
              APPENDIX G.--Sample DLG Data File
         (Optional Distribution Format)--continued


L    6     8     7     9     1                 2     0     0
   687842.44  3819301.46   687735.78  3819299.29
L    7     9     8    10     1                 2     0     0
   687969.42  3819304.04   687842.44  3819301.46
L    8    10     9    11     1                 2     0     0
   688042.96  3819310.62   687969.42  3819304.04
L    9    11    10    12     1                 2     0     0
   688129.40  3819307.29   688042.96  3819310.62
L   10    12    11    13     1                 2     0     0
   688462.08  3819314.06   688129.40  3819307.29
L   11    13    12    14     1                 2     0     0
   688632.22  3819317.52   688462.08  3819314.06
L   12    14    13    15     1                 2     0     0
   688837.92  3819321.70   688632.22  3819317.52
L   13    15    14    16     1                 2     0     0
   688947.12  3819323.92   688837.92  3819321.70
L   14    16    15    17     1                 2     0     0
   689490.57  3819334.97   688947.12  3819323.92
L   15    17    16    18     1                 2     0     0
   690620.63  3819357.95   689490.57  3819334.97
L   16    18    17    18     1                 2     0     0
   690925.37  3819364.15   690620.63  3819357.95
L   17    19    18    19     1                 2     0     0
   691189.48  3819369.52   690925.37  3819364.15
L   18    20    19    20     1                 2     0     0
   691605.95  3819377.98   691189.48  3819369.52
L   19    21    20    21     1                 2     0     0
   693447.02  3819417.96   691605.95  3819377.98
L   20    22    21    21     1                 2     0     0
   694107.34  3819428.85   693447.02  3819417.96
L   21    23    22    22     1                 2     0     0
   694914.90  3819445.27   694107.34  3819428.85
L   22    24    22    21    22                 3     1     0
   694205.18  3819364.78   694194.61  3819384.89   694107.34  3819428.85
   170   205
L   23    25     3     5     4                 3     1     0
   684825.58  3819113.09   684849.22  3819199.95   684845.86  3819240.53
   170   209
L   24    26    14    15    16                 2     1     0
   688848.53  3819174.57   688837.92  3819321.70
   170   210
L   25    27    26    25    16                 2     1     0
   688901.91  3819173.11   688848.53  3819174.57
   170   210
L   26    27    15    16    17                 3     1     0
   688901.91  3819173.11   688939.85  3819181.50   688947.12  3819323.92
   170   210
L   27    28    17    18    18                 3     1     0
   690593.10  3819212.58   690628.40  3819226.00   690620.63  3819357.95
   170   209
              APPENDIX G.--Sample DLG Data File
         (Optional Distribution Format)--continued


L   28    29    25     4     4                 3     1     0
   685461.28  3819085.37   685414.90  3819117.45   684825.58  3819113.09
   170   209
L   29    30    24    24    22                 2     1     0
   694605.90  3819273.85   694205.18  3819364.78
   170   205
L   30    30    23    22    23                 4     1     0
   694605.90  3819273.85   694615.85  3819284.21   694851.82  3819423.66
   694914.90  3819445.27
   170   205
L   31    31    12    13    14                 4     1     0
   688529.54  3819119.81   688480.67  3819149.30   688470.15  3819166.87
   688462.08  3819314.06
   170   210
L   32    31    13    14    15                 4     1     0
   688529.54  3819119.81   688611.12  3819230.71   688637.82  3819292.23
   688632.22  3819317.52
   170   210
L   33    32    21    21    21                 2     1     0
   693453.44  3819227.55   693447.02  3819417.96
   170   209
L   34    33     4     3     6                 4     1     0
   687148.37  3819076.48   687139.15  3819155.05   687123.40  3819180.14
   687098.38  3819286.33
   170   210
L   35    33     5     6     7                 4     1     0
   687148.37  3819076.48   687172.89  3819120.17   687342.68  3819265.89
   687347.30  3819288.85
   170   201

Major Code                        Base Category
                                                                          

020Hypsography

050Combined hydrography--streams, water bodies, and wetlands

090Boundaries

l70*Transportation systems--roads and trails 

l80*Transportation systems--railroads

l90*Transportation systems--pipelines, transmission 
  lines, and miscellaneous transportation

300U.S. Public Land Survey System

                                                                          

*Transportation systems have been assigned more than one major code so that
their components may be readily separated for analytical applications.


                                                                           
            Nodes                                  Areas
                                                                           

Number   X Coordinate   Y Coordinate   Number   X Coordinate   Y Coordinate

Nl           l             28            Al          0               0     
N2          l3             l4            A2          6              24   
N3          23             28            A3          3              l0  
N4          l3              l            A4          8               7  
N5          l3              7            A5         l8              l4  
N6          22             l0
N7           6              5
N8          l0              4
N9          ll             24
Nl0         23              l
Nll          l             l7
Nl2          l              l
N13          9              9
                                                                           


                         Lines

                                                                          

          Nodes                  Area                Coordinates        
Number   Starting  Ending    Left     Right   (first x y      last x y)

Ll        l          3        l        2         l, 28         23, 28
L2        3         l0        l        5        23, 28         23,  l
L3        4         l2        l        3        l3,  l          l,  l
L4       ll          2        2        3         l, l7  ....   l3, l4
L5        2          3        2        5        l3, l4         23, 28
L6        2          5        5        3        l3, l4         l3,  7
L7        5          4        5        3        l3,  7         l3,  l
L8       13          7        4        3         9   9  ....    6,  5
L9        7          8        4        3         6,  5  ....   l0,  4
Ll0       4         l0        5        1        l3,  1         23,  l
Lll       5          6        5        5        l3,  7  ....   22, l0
Ll2       9          9        2        2        ll, 24         ll, 24
Ll3      l2         ll        l        3         l,  l          l, l7
Ll4      ll          l        l        2         l, l7          l, 28
L15       8         13        4        3        10,  4  ....    9,  9
                                                                          


CARTERSVILLE                 GA          1981,        100000.  S01
RO4.HYS01
     3     1    16  -0.840560150000038D+08   0.340260150000010D+08   0.0
                     0.0                     0.0
   0.0                     0.0                     0.0
   0.0                     0.0                     0.0
   0.0                     0.0                     0.0
   0.0                       2   0.254000000000000D+01     0     4
  -0.850000000000000D+02   0.343750000000000D+02  -0.850000000000000D+02
   0.345000000000000D+02  -0.848750000000000D+02   0.345000000000000D+02
  -0.848750000000000D+02   0.343750000000000D+02

   0.253948017060000D+01  -0.516359320290000D-01   0.689504506100000D+06
   0.381240214830000D+07     4
SW -2263 -2729NW -2260  2729NE  2259  2729SE  2263 -2729

     1

HYDROGRAPHY            795   118   795    22   530   138

N      6 -2034  1365     1     0

N      7 -2260  1285     0     0

N      8 -2261  1263     0     0

N     11 -1698  1059     0     0

N     15 -1292   929     1     0

    50     5

N     72 -2260  1855     0     0

N     73 -2217  1836     1     0

N     74 -2259  1824     0     0

N     77 -2087  1707     1     0

N     80 -2077  1584     0     0

N     88 -1200   821     0     0

N     90 -1244   608     1     0

    50     4

A      1     0     0     1     0

     0     0

A      4     0     0     0     0

A      5 -2057  1523     1     0

    50   412

A      6     0     0     0     0

A      8 -1243   770     1     0

    50   421

L      6    11     6     4     4    21     1     0

 -1698  1059 -1699  1115 -1686  1140 -1686  1178 -1698  1193 -1718  1203
 -1777  1216 -1792  1238 -1838  1257 -1902  1243 -1910  1236 -1911  1212
 -1920  1208 -1929  1214 -1957  1249 -1957  1253 -1981  1281 -2010  1333
 -2009  1351 -2014  1361 -2034  1365
    50   412

L      7    15    11     4     4    17     1     0

 -1292   929 -1295   951 -1306   973 -1308   987 -1321  1000 -1359  1019
 -1416  1017 -1430  1008 -1434  1000 -1455   981 -1469   988 -1482  1000
 -1524   994 -1576  1002 -1644  1034 -1669  1050 -1698  1059

    50   412

L     55    73    72     5    18     2     1     0

 -2217  1836 -2260  1855

    50   606

L     58    77    73     5     4     5     1     0

 -2087  1707 -2116  1746 -2164  1801 -2213  1828 -2217  1836

    50   606

L     66     6    77     5     4     7     1     0

 -2034  1365 -2036  1520 -2052  1573 -2053  1586 -2065  1609 -2069  1643
 -2087  1707
    50   606

L     68     74     7     1     6     2     0     0

 -2260  1285 -2259  1824
                                                                    
L     70     74    80     6     5    10     1     0

 -2260  1285 -2207  1277 -2123  1284 -2103  1292 -2077  1315 -2063  1355
 -2058  1375 -2060  1472 -2063  1523 -2077  1584
    50   605

L     69    80     7     6     5    11     1     0

 -2077  1584 -2082  1616 -2085  1619 -2087  1637 -2094  1652 -2098  1675
 -2107  1695 -2161  1763 -2209  1801 -2244  1820 -2259  1824
    50   605

L     72     8     6     5     4     7     1     0

 -2261  1263 -2192  1254 -2142  1256 -2106  1267 -2073  1283 -2044  1335
 -2034  1365
    50   606

L     80    90    15     4     8    14     1     0

 -1244   608 -1248   611 -1251   661 -1260   707 -1259   737 -1268   749
 -1292   765 -1289   779 -1268   824 -1268   843 -1276   858 -1281   883
 -1299   918 -1292   929

    50   200

L     81    90    88     8     4    12     1     0

 -1244   608 -1228   613 -1193   699 -1181   716 -1167   724 -1167   730
 -1180   743 -1198   769 -1196   787 -1179   802 -1177   810 -1200   821
    50   200

L     82    88    15     8     4    8      1     0

 -1200   821 -1200   848 -1200   854 -1202   864 -1202   875 -1260   898
 -1274   930 -1292   929
    50   200
                                                                          

                                                                 
                      Standard           Optional

Character set        8-bit ASCII        8-bit ASCII

Logical record
 length              144 bytes          80 bytes

Physical record      variable in        variable in
 length (blocksize)    multiples of       multiples of
                       144 bytes          80 bytes

Coordinate system    internal file      ground 
             (thousandths of    planimetric
             a map inch)        (UTM)

Topological          contained only     contained in
 linkages              in line elements   node, area, and
                                          line elements
                                                                 

These formats are described in detail in Appendixes A and B.



F01F02F03F04

                                                                          
F05F06F07F08
                                                                          

A 1:100,000-scale quad divided into eight 15-minute quads, 4 per 30-minute
area.


                                                                          
S01S02S03S04S05S06S07S08
                                                                          
S09S10S11S12S13S14S15S16
                                                                          
S17S18S19S20S21S22S23S24
                                                                          
S25S26S27S28S29S30S31S32
                                                                          

A 1:100,000-scale quad divided into 32 7.5-minute quads, 16 per 30-minute
area.

 
