USGS

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/



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