Description of MBGEOLSE Digital Database from USGS MF-2345



by

Florence L. Wong

U.S. Geological Survey, Menlo Park, California



1. INTRODUCTION



     This document describes the digital data layer MBGEOLSE that 

appears in the map "Seafloor rocks and sediments of the continental 

shelf from Monterey Bay to Point Sur, California" by Eittreim and 

others (2000). The data are based on acoustic swath (side-scan sonar) 

mapping of the greater Monterey Bay area continental shelf from Point 

A–o Nuevo to Point Sur (Eittreim and others, 2001).  This is one of 

several files that make up the publication and should be viewed in 

conjunction with the rest, which are available from the World Wide Web 

at http://geopubs.wr.usgs.gov/map-mf/mf2345.



     For those interested in the geology of the mapped area who do not use an 

ARC/INFO compatible Geographic Information System (GIS), this web page also 

lists two plotfiles containing the map publication that uses this database.  

MF2345.EPS is in postscript format and MF2345PR.PDF is in print-optimized 

Acrobat portable document format. For viewing on a computer monitor, a small 

view graphic MF2345.GIF and a screen-optimized Acrobat portable document 

MF2345SC.PDF are provided.



     Those without computer capability can obtain plots of the map files 

through the USGS plot-on-demand service for digital geologic maps (U.S. 

Geological Survey, Map Distribution, Box 25286, Federal Center, Denver, CO 

80225 or by calling the Earth Science Information Center in Denver at 303-

202-4200) or through an outside vendor.



2. DIGITAL DATABASE FORMAT



     The data in this report were compiled in ARC/INFO, a commercial 

geographic information system (Environmental Systems research 

Institute, Redlands, California).  The files are in COVERAGE (ARC/INFO 

vector data) or INFO database format and are viewable only with 

ARC/INFO or ArcView.  The coverage is stored in uncompressed ARC 

export format (ARC/INFO version 8.0.2).  ARC/INFO export files (with 

the .e00 extension) can be converted into ARC/INFO coverages with the 

import tool in either ARC/INFO or ArcView.



3. DIGITAL COMPILATION



     Sidescan sonar images are collected in rectangular strips with 

widths depending on water depth and instrument specifications (see 

explanatory text on map sheet or MF2345.TXT).  Image processing 

techniques are used to rectify and register the images and mosaic 

adjacent image strips into a continuous image.  Registered mosaics 

prepared from data for each of several survey cruises were processed 

in small areas with geographic information stored in the header and in 

an accompanying ASCII file.  The images were converted to TIFF format 

and a world file was constructed from the header information.  The 

resolution of the sidescan sonar images range from 40 cm to 2.5 m.  

Interpretation was done in Adobe Photoshop at a scale of 2.4 m per 

pixel. At an image resolution of 72 dpi, common to most video screens, 

this represents a scale of 1:6,800. As each area mosaic was processed, 

the sidescan image file was opened in Adobe Photoshop as a base layer. 



     The geologic interpretation was drawn in an overlayer with 

transparent brush tools and index colors, a different color for each 

map unit.  The completed interpretation was saved as a TIFF image.  

This interpretation was converted to a spatially registered grid in 

ARC/INFO and the grid into a polygon coverage.  The grid-code item 

from the grid attribute table (.vat) was retained as the polygon type.  

ARC/INFO's Arcedit application was used for additional labeling and 

cleanup.  As successive pieces of the data became available, they were 

joined to the master coverage mbgeolse. The stepped appearance of the 

line features was not smoothed because the smoothing algorithm 

collapsed some of the smaller polygons.



4. DATABASE SPECIFICS



     The map database consists of an ARC/INFO coverage and supporting 

INFO database files.  The coverage is stored in the Universal 

Transverse Mercator (UTM) coordinate system with the following 

parameters:  



Projection                  UTM

Zone                         10

Datum                     NAD83

Units                    METERS

Spheroid                GRS1980





     Digital tics define a 7.5-minute grid of latitude and longitude 

corresponding to standard quadrangle corners. The rectangular window 

represented by the bounding coordinates covers 52 x 97 km or 

approximately 5,000 square kilometers.  The actual data area covers 

1,200 square kilometers on the shelf off the central California coast 

between Point Ano Nuevo and Point Sur.



              UTM meters      Geographic units

XMIN        555325.56704    -122.38432

YMIN       4010100.50000      36.22983

XMAX        607248.72985    -121.79294

YMAX       4107577.06941      37.11289





     The content of the geologic database can be described in terms of 

the lines and the areas that compose the map.  Descriptions of the 

database fields use the following terms:



ITEM NAME   name of the database field (item)

WIDTH       maximum number of digits or characters stored

OUTPUT      number of digits or characters in output

TYPE        B-binary integer, F-binary floating point number,

             I-ASCII integer, C-ASCII character string

N. DEC.     number of decimal places maintained for floating

             point numbers





4.1 Lines 



     The lines (arcs) are recorded as strings of vectors and define 

the boundaries of the map units and linear structures, such as faults. 

This information is recorded in the LTYPE field of the arc attribute 

table MBGEOLSE.AAT:

 

ITEM NAME    WIDTH OUTPUT  TYPE N.DEC

FNODE#          4     5     B      -   starting node of arc

TNODE#          4     5     B      -   ending node of arc

LPOLY#          4     5     B      -   polygon to left of arc

RPOLY#          4     5     B      -   polygon to right of arc

LENGTH          8    18     F      5   length of arc in meters

MBGEOLSE#       4     5     B      -   unique internal control number

MBGEOLSE-ID     4     5     B      -   user-assigned sequence number

LTYPE          15    15     C      -   line type



Unique values of LTYPE in mbgeolse are contact, scratch, and fault.





4.2 Polygons



     Map units (polygons) are described in the polygon attribute table 

MBGEOLSE.PAT.  The GRID-CODE field of mbgeolse.pat contains a number that is 

linked to the identity of the map unit in the lookup table MBGEOLSE.PLUT.  

Map units are described more fully in the text (reproduced in MF2345.TXT) of 

the map sheet and in Eittreim and others (2001).



ITEM NAME   WIDTH OUTPUT  TYPE N.DEC

AREA            8    18     F      5   area of polygon, square meters

PERIMETER       8    18     F      5   perimeter of polygon, meters

MBGEOLSE#       4     5     B      -   unique internal control number

MBGEOLSE-ID     4     5     B      -   user-assigned sequence number

GRID-CODE       4     8     B      -   value keyed to lookup table

                                         MBGEOLSE.PLUT below

TAG             2     4     B      -   = 1 to flag polygon for

                                         1:100,000-scale plots





4.3 Polygon symbol lookup table



     The column definitions for the polygon lookup table MBGEOLSE.PLUT 

are



ITEM NAME    WIDTH OUTPUT  TYPE N.DEC

GRID-CODE        4     8     B      -  polygon label from mbgeolse.pat

DESCRIPTION     35    25     C      -  rock type or formation

AGE             26    26     C      -  geologic age

PTYPE            5     5     C      -  geologic symbol

**  REDEFINED ITEMS  **

LABEL            5     5     C      -  alternate name for PTYPE



The contents of the lookup table are listed here and described in 

Eittreim and others (2001).



GRID-CODE DESCRIPTION               AGE                        PTYPE

      -9  nodata

       0  universe polygon (nodata)

       1  Monterey Formation        Miocene                    Tm

       2  mud and fine sand         Quaternary                 Qmud

       3  coarse sands and gravel   Quaternary                 Qsd

       4  granitic rock             Late Cretaceous            Kgr

       5  pipeline

       8  relict gravels            Quaternary                 Qgv

       9  Santa Cruz Mudstone       late Miocene               Tsc

      10  Purisima Formation        Pliocene and Miocene       Tp

      13  Aromas Sand               Quaternary                 Qa

      15  Rocks of Sur platform     Tertiary and Cretaceous    TKu

      28  Vaqueros(?) Formation     Miocene and late Oligocene Tv(?)





REFERENCES CITED:



Eittreim, S.L., Anima, R.J., and Stevenson, A.J., 2001,  Seafloor 

geology of the Monterey Bay area continental shelf, in Eittreim, S.L., 

and Noble, M.A., editors, Seafloor Geology and Natural Environment of 

the Monterey Bay National Marine Sanctuary: Marine Geology, in press.



Eittreim, S.L., Anima, R.J., Stevenson, A.J., and Wong, F.L., 2000, 

Seafloor rocks and sediments of the continental shelf from Monterey 

Bay to Point Sur, California: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-2345, 1 sheet, scale 1:100,000 and accompanying 

digital database, http://geopubs.wr.usgs.gov/map-mf/mf2345.





Any use of trade, product, or firm names in this publication is for 

descriptive purposes only and does not imply endorsement by the U.S. 

Government.