Digital Data Sets Describing Principal Aquifers, Surficial Geology,
and Ground-Water Regions of the Conterminous United States
By Rick M. Clawges and Curtis V. Price
U.S. Geological Survey Open-File Report 99-77
Rapid City, South Dakota
1999
TABLE OF CONTENTS
Introduction
Acknowledgment
File Formats
ARC/INFO format files
DLG format files
SDTS format files
Data Organization
Data-Set Documentation
Geometric Registration
Notes
References Cited
INTRODUCTION
This report contains digital data sets describing principal aquifers, surficial
geology, and ground-water regions of the conterminous United States. The
data source for the principal aquifers and surficial geology data sets
is "The National Atlas of the United States of America" (U.S. Geological
Survey, 1970; Hunt, 1979). The data source for the ground-water regions
data set is "Ground-Water Regions of the United States" by Heath (1984).
Some of the digital lines describing coastlines were modified from U.S.
Geological Survey boundary information (U.S. Geological Survey, 1990; Lanfear,
1984). Because most of the source materials do not cover Alaska and Hawaii,
only the conterminous 48 states are included in these data sets.
Compilation of the data sets was supported by the National Water-Quality
Assessment (NAWQA) Program of the U.S. Geological Survey (USGS). The objectives
of the NAWQA Program are to: (1) describe current water-quality conditions
for a large part of the Nation's freshwater streams, rivers, and aquifers,
(2) describe how water quality is changing over time, and (3) improve the
understanding of the primary natural and anthropogenic factors that affect
water-quality conditions. National analysis of data, based on aggregation
of comparable information obtained from across the United States, is a
major component of the NAWQA Program. The data sets included in this report
were created in support of NAWQA national data analysis activities.
ACKNOWLEDGMENT
The authors thank Brenda Athow of the U.S. Geological Survey for her work
in the creation and initial processing of the principal aquifers and surficial
geology data sets.
FILE FORMATS
The data sets were processed using the ARC/INFO Version
7.1.1 software package (Environmental Systems Research Institute, 1997).
The data sets are stored in three formats: ARC/INFO export, DLG, and SDTS.
ARC/INFO export is a proprietary format copyrighted by Environmental Systems
Research Institute (ESRI), Inc., Redlands, California.
ARC/INFO FORMAT FILES
The data sets stored in ARC/INFO export format have the file extension
".E00". ARC/INFO export files allow for transfer of spatial data sets created
in ARC/INFO format from one ESRI-supported computer platform to another.
DLG FORMAT FILES
The data sets stored in the public-domain Digital Line Graph Version 3
(DLG-3) Optional format have the file extension ".DLG". The DLG-3 format,
which was designed for data interchange, stores spatial data organized
in a polygon or line data structure. The topological linkages are explicitly
encoded for node, area, and line elements. The files are composed of 8-bit
ASCII characters organized into fixed logical records of 80 bytes. A detailed
description of the DLG-3 Optional format may be found in Data Users Guide
3, Digital Line Graphs from 1:2,000,000-Scale Maps (U.S. Geological Survey,
1990). The DLG file format can be read by a variety of computer programs.
In the DLG-format version of these data sets, the attributes are coded
by setting the DLG major code to zero and the minor code to an integer
column used to relate to the provided attribute tables. The attribute tables
are provided as comma-delimited ASCII files with file extension ".ATT".
These files include the column names in the first record and all the attribute
data in subsequent records. The first column corresponds to the minor codes
used in the DLG file.
The following table shows the relationship between the DLG files and
the attribute files:
| DLG file |
Features |
Attribute file |
| AQUIF75M.DLG |
polygons |
AQUIF75M.ATT |
| GEOL75M.DLG |
polygons |
GEOL75M.ATT |
| GWREGION.DLG |
polygons |
GWREGION.ATT |
| GWREGION.DLG |
lines |
GWREGIO2.ATT |
| GWREGUW.DLG |
polygons |
GWREGUW.ATT |
| GWREGUW.DLG |
lines |
GWREGUW2.ATT |
SDTS FORMAT FILES
The data sets stored in the public-domain Spatial Data Transfer Standard
(SDTS) format have the file extension ".TGZ". SDTS (U.S. Geological Survey,
1998) is a large standard composed of smaller, more limited subsets that
are Federally approved as part of the SDTS FIPS 173 standard. These subsets
are called profiles. The profile created for the data sets in this report
are part of the Topological Vector Profile designed specifically for planar
vector data with topology.
These files have been archived using the UNIX "tar.exe"
command and then compressed using the "gzip"
program. They can be extracted using the following command line on UNIX
and NT systems:
gunzip -c filename.tgz | tar xvof -
Other compressed files (with a ".gz" extension) can be uncompressed
using the gunzip command:
gunzip filename.gz
This command will uncompress the file and restore its original name.
For example: "AQUIF75M.DLG" or "AQUIF75M.E00".
At the time of preparing this report, PC-compatible viewer programs
that can read many public-domain formats, including DLG and SDTS, were
available online at:
ftp://ftpmcmc.er.usgs.gov/release/dlgview/data/usgsview.exe
ftp://ftpmcmc.er.usgs.gov/release/viewers/
DATA ORGANIZATION
A_NOTICE.TXT
Liability disclaimer
AQUIF75M
Complete documentation
of the data sources and procedures use to create the principal aquifers
data set
and links for
retrieval of the data set.
GEOL75M
Complete documentation
of the data sources and procedures use to create the surficial geology
data set
and links for
retrieval of the data set.
GWREGION
Complete documentation
of the data sources and procedures use to create the ground-water regions
data set
and links for
retrieval of the data set.
GWREGUW
Complete documentation
of the data sources and procedures use to create the ground-water regions
with
unconsolidated
watercourses data set and links for retrieval of the data set.
DATA-SET DOCUMENTATION
A structured documentation file (known as "formal metadata") for each data
set is provided. This file is named the same as the data set, with a file
extension of ".TXT". The documentation files comply with the Federal Geographic
Data Committee (FGDC) Content Standards for Digital Geospatial Metadata
(Federal Geographic Data Committee, 1994, 1998). The FGDC-compliant metadata
files contain detailed descriptions of the data sets and include narrative
sections describing the procedures used to produce the data sets in digital
form. The metadata also includes detailed references of the sources used
to create the data set.
GEOMETRIC REGISTRATION
The Albers Equal Area map projection (Snyder, 1987) was chosen for the
data sets. This projection is appropriate for maps of the conterminous
United States because of the visual presentation and equal-area characteristics,
which facilitate areal analysis. The projection is cast on the North American
Datum of 1927.
Albers Equal Area projection parameters
| Projection parameters: |
| Spheroid |
Clarke Ellipsoid 1866 |
| Datum |
North American Datum 1927 |
| First standard parallel |
29 30' 00" North |
| Second standard parallel |
45 30' 00" North |
| Central meridian |
96 00' 00" West |
| Latitude of projection origin |
23 00' 00" North |
| Coordinate system parameters |
| False easting |
0.0 |
| False northing |
0.0 |
| Planimetric units of measure |
Meters |
NOTES
Use of trade names is for descriptive purposes only, and does not imply
endorsement by the U.S. Government.
REFERENCES CITED
Environmental Systems Research Institute, Inc. (ESRI), 1997, ARC/INFO 7.1.1
Help: Redlands, Calif., ESRI, [on-line documentation].
Federal Geographic Data Committee, 1994, Content standards for digital
geospatial metadata (June 8): Washington, D.C., Federal Geographic Data
Committee, 78 p., accessed July 21, 1998, at URL http://www.fgdc.gov/Metadata/ContStan.html
Federal Geographic Data Committee, 1998, Content standards for digital
geospatial metadata, standard FGDC-STD-001-98: Washington, D.C., Federal
Geographic Data Committee, 78 p., accessed December 27, 1998, at URL http://www.fgdc.gov/metadata
Heath, R.C., 1984, Ground-water regions of the United States: U.S. Geological
Survey Water-Supply Paper 2242, 78 p.
Hunt, Charles D., 1979, National Atlas of the United States of America--
Surficial Geology: U.S. Geological Survey, NAC-P-0204-75M-O, [map].
Lanfear, K.J., 1984, Digital map of counties and county equivalents
in the conterminous United States: U.S. Geological Survey data available
on the World Wide Web, accessed July 21, 1998, at URL http://water.usgs.gov/lookup/getspatial?county2m
Snyder, J.P., 1987, Map projections--A working manual: U.S. Geological
Survey Professional Paper 1395, 383 p.
U.S. Geological Survey, 1970, The National Atlas of the United States
of America: Washington, D.C., U.S. Government Printing Office, 417 p.
______, 1990, Digital line graphs from 1:2,000,000-scale maps, data
users guide 3: U.S. Geological Survey National Mapping Program Technical
Instructions, 70 p., accessed July 21, 1998, at URL ftp://mapping.usgs.gov/pub/ti/DLG/2mdlgguide/
______, 1998, SDTS Home Page: U.S. Geological Survey, accessed July
21, 1998, at URL http://mcmcweb.er.usgs.gov/sdts/
