USGS

Digital Data Sets Describing Water Use, Toxic Chemical Releases, Metropolitan Areas, and Population Density of the Conterminous United States

By Curtis V. Price and Rick M. Clawges

U.S. Geological Survey Open-File Report 99-78

Rapid City, South Dakota
1999
 

TABLE OF CONTENTS

Introduction
File Formats
   ARC/INFO format files
   DLG and DEM format files
   SDTS format files
Data Organization
Data-Set Documentation
Geometric Registration
Notes
References Cited
 

INTRODUCTION

This report contains digital data sets describing water use, toxic chemical releases, metropolitan areas, and population density of the conterminous United States. The data source for the water-use data is from the U.S. Geological Survey (USGS) (U.S. Geological Survey, 1990, 1998b; Lanfear, 1984). The toxic chemical release information is from the U.S. Environmental Protection Agency (1997, 1998), and the metropolitan area and population density data sets were derived from data provided by the U.S. Bureau of the Census (1995) and the Consortium for International Earth Science Information Network (1995). 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. 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 for NAWQA national data analysis activities.

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. In the special case of the population density data set, the USGS DEM and ASCIIGRID formats are used in lieu of DLG and SDTS.

ARC/INFO FORMAT FILES

The data sets stored in ARC/INFO export format have the file extension "E00". ARC/INFO export files allow transfer of spatial data sets created in ARC/INFO format from one ESRI-supported computer platform to another.

The file "POPDENGA.GZ" is an ASCII file representing the population density data set "popdeng" in a format produced by the ARC/INFO GRIDASCII command. The file has been compressed using the "gzip" program, and can be extracted using the gunzip command:

 gunzip popdenga.gz

 The ASCIIGRID format file is included so users that cannot read the gridded data in other formats can write a simple computer program to convert the data into a format they can use. The format of the file includes a set of keywords and parameters describing the georeferencing of the data set (the location of the grid as referenced to the earth), for example:
 
 
Keyword Parameter Description
ncols 4521 Number of rows in the grid
nrows 2898 Number of columns in the grid
xllcorner -2462303.66 X-coordinate of lower left corner of grid
yllcorner 176796.66 Y-coordinate of lower left corner of grid
cellsize 1055.35 Grid cell size
NODATA_value -9999 Grid cells with no valid data value
 
This header information is followed by the grid data values, one record per row, starting at the upper left corner of the grid.
 

DLG  AND DEM 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. The DEM format is designed for representation of grid-cell data and has a physical and logical record length of 1024 characters. A detailed description of the DLG-3 Optional and DEM formats may be found in Data Users Guides published by the USGS  (U.S. Geological Survey, 1990, 1993). The DLG and DEM file formats 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 geographic features 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 and DEM files and the attribute files:
 
File name Features Attribute file
COWU95.DLG polygons COWU95.ATT
EFTRI.DLG points EFTRI.ATT
METROPOP.DLG polygons  METROPOP.ATT
POPDENGD.GZ grid cell (no attribute file)
 

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: "COWU95.DLG" or "COWU95.E00".

At the time of preparing this report, PC-compatible viewer programs that can read many public-domain formats, including DEM, 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
COWU95
          Complete documentation of the data sources and procedures use to create the county water-use data set
          and links for retrieval of the data set.
EFTRI
          Complete documentation of the data sources and procedures use to create the USEPA Envirofacts Toxic Release Inventory data set
          and links for retrieval of the data set.
METROPOP
          Complete documentation of the data sources and procedures use to create the metropolitan areas data set
          and links for retrieval of the data set.
POPDENG
          Complete documentation of the data sources and procedures use to create the population density 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

Consortium for International Earth Science Information Network (CIESIN), 1995, Socioeconomic Data and Applications Center (SEDAC), Archive of Census Related Products: CIESIN/SEDAC, accessed July 21, 1998 at URL http://sedac.ciesin.org/plue/cenguide.html

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

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. Bureau of the Census, 1995, County and city data book: 1994, CD-CCDB-94, Washington, D.C., [cd-rom disk].

U.S. Environmental Protection Agency, 1997, 1987-1995 Toxics Release Inventory, EPA 749-C-97-003, Washington, D.C., [cd-rom disk].

U.S. Environmental Protection Agency, 1998, Envirofacts Warehouse Homepage: U.S. Environmental Protection Agency, accessed February 20, 1998, at URL http://www.epa.gov/enviro/

U.S. Geological Survey, 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/

______, 1993, Digital elevation models, data users guide 5: U.S. Geological Survey National Mapping Program Technical Instructions, 38 p., accessed July 21, 1998, at URL ftp://mapping.usgs.gov/pub/ti/DEM/demguide/

______, 1998a, SDTS Home Page: U.S. Geological Survey, accessed July 21, 1998, at URL http://mcmcweb.er.usgs.gov/sdts/

______, 1998b, Water use in the United States: U.S. Geological Survey, accessed July 21, 1998, at URL http://water.usgs.gov/watuse/

 




U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/ofr99078
Page Contact Information: GS Pubs Web Contact
Last modified: Thursday, January 10 2013, 11:08:39 PM
FirstGov button  Take Pride in America button