USGS Oklahoma District GREDS

Water Resources of Oklahoma

GCIP Reference Data Set (GREDS)

By Alan Rea and Joel R. Cederstrand
U.S. Geological Survey
Open-File Report 94-388
Oklahoma City, Oklahoma, U.S.A.
1994

Abstract

The data sets on this compact disc are a compilation of several geographic reference data sets of interest to the global-change research community. The data sets were chosen with input from the Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project (GCIP) Data Committee and the GCIP Hydrometeorology and Atmospheric Subpanels. The data sets include: locations and periods of record for stream gages, reservoir gages, and meteorological stations; a 500-meter-resolution digital elevation model; grid-node locations for the Eta numerical weather-prediction model; and digital map data sets of geology, land use, streams, large reservoirs, average annual runoff, average annual precipitation, average annual temperature, average annual heating and cooling degree days, hydrologic units, and state and county boundaries. Also included are digital index maps for LANDSAT scenes, and for the U.S. Geological Survey 1:250,000, 1:100,000, and 1:24,000-scale map series. Most of the data sets cover the conterminous United States; the digital elevation model also includes part of southern Canada. The stream and reservoir gage and meteorological station files cover all states having area within the Mississippi River Basin plus that part of the Mississippi River Basin lying within Canada. Several data-base retrievals were processed by state, therefore many sites outside the Mississippi River Basin are included.

Introduction

This Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project (GCIP) Reference Data Set (GREDS) compact disc contains several geographic reference data sets of interest to the global-change research community. The data sets were chosen with input from the GCIP Data Committee and the GCIP Hydrometeorology and Atmospheric Subpanels. The data sets include: locations and periods of record for stream gages, reservoir gages, and meteorological stations; a 500-meter-resolution Digital Elevation Model (DEM); grid-node locations for the Eta numerical weather prediction model; and digital map data sets of geology, land use, streams, large reservoirs, average annual runoff, average annual precipitation, average annual temperature, average annual heating and cooling degree days, hydrologic units, and state and county boundaries. Also included are digital index maps for LANDSAT scenes, and for the U.S. Geological Survey (USGS) 1:250,000, 1:100,000, and 1:24,000-scale map series. A listing of Hydro-Climatic Data Network (HCDN) stream gages (Slack and others, 1993) also is included and may be related to the stream-gage site file for locations and other information.

Most of the data sets cover the conterminous United States; the DEM also includes part of southern Canada. The stream and reservoir gage and meteorological station files cover all states having area within the Mississippi River basin, plus that part of the Mississippi River Basin lying within Canada. Several data-base retrievals were processed by state, therefore many sites outside the Mississippi River Basin are included.

A documentation file accompanies each data set, indicating the source of the data, time frame with which it is associated, and other information. The stream gages, reservoir gages, and meteorological stations are divided into two separate files for currently operating or historical (discontinued) sites; sites with data for 1993 or later (1992 for the Canadian hydrometric sites) are considered currently operating unless otherwise indicated. Sites may be discontinued at any time. The agency responsible for a site should be contacted to determine if the sites are operational.

The data sets are provided in at least two formats: a generic or public-domain format; and ARC/INFO export files. (Use of trade names is for descriptive purposes only, and does not imply endorsement by the U.S. Government. ARC/INFO software was used in the development of these data sets, and these original-format files are provided for the convenience of users, in addition to the generic or public-domain format files.) The DEM is provided in ARC/INFO Grid (version 7.0.2) format, rather than export-file format.

Graphic images of the data sets also are provided in Graphics Interchange Format (GIF) files. GIF files are easily displayed on a variety of computer systems using readily available display software. These images provide a simplified view of the data sets available on this disc, and may be used for browsing purposes. The GIF files in all cases portray significantly less spatial resolution and information content than the actual data sets.

Compilation and publication of this compact disc was funded by the USGS Global-Change Research Program.

Disc Organization

This disc complies with the ISO 9660 standard for CD-ROM discs. It is intended for use with personal computers using the MS-DOS operating system. The disc is compatible with UNIX, Macintosh, and VAX computers equipped with the appropriate CD-ROM reader and software. All ASCII files, including Digital Line Graph (DLG) files and ARC/INFO export files, use MS-DOS record delimiters (carriage-return, line-feed). Conversion of record delimiters in these files may be necessary for operating systems other than MS-DOS. The overall layout of the disc is:

\----- a_readme.1st    This file
    |
    |
    |- basins\       Hydrologic units of the conterminous United States,
    |                   plus the boundary of the Mississippi River Basin
    |                   in Canada
    |
    |- browse\       GIF images for browsing
    |
    |
    |- climate\      Climatography of the United States, maps of 1961-90
    |                  normal temperature, precipitation, and degree days
    |
    |- etamodel\     Grid-node locations and description of the Eta model
    |
    |
    |- geology\      Geology of the conterminous United States at 
    |                  1:2,500,000 Scale
    |
    |- maps\         State and county boundaries, quadrangle index maps,
    |                  conterminous United States
    |
    |- landsat\      Scene boundaries for LANDSAT paths and rows,
    |                  conterminous United States and southern Canada
    |
    |- landuse\      Major land uses in the United States
    |
    |
    |- resrvoir\     Large reservoirs of the United States
    |
    |
    |- rivers\       U.S. Environmental Protection Agency river-reach 
    |                  file (RF-1)
    |
    |- runoff\       Average annual runoff in the United States
    |
    |
    |- sites\        Locations of stream gages, reservoir gages, and
    |                  meteorological stations, Mississippi River Basin

    |
    |- software\     Programs for handling map projections
    |                  and compressed files
    |
    |- terrain\      Digital Elevation Model of the conterminous United 
    |                  States and southern Canada, 500-meter resolution
    |
    |- xportarc\     ARC/INFO export files of the above data sets

Data-Set Documentation

A README.TXT file exists in each directory, and provides an overview of the contents of the files or subdirectories in the directory. A documentation file for each data set is located in the directory with the data set, and is named with a file extension of ".DOC". The documentation files comply with the Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata, dated June 8, 1994. The FGDC-compliant metadata files are very detailed descriptions of the data sets, and include a narrative section describing the procedures used to produce the data set in digital form. The FGDC-compliant metadata files are plain ASCII text files.

The ARC/INFO export-file versions of each data set contain the documentation information used to create the FGDC-compliant metadata files. The DOCUMENT program, an ARC Macro Language (AML) program jointly developed by the USGS, the U.S. Environmental Protection Agency (USEPA), and Environmental Systems Research Institute (ESRI) may be used to display, reference, or update the data set documentation files. The DOCUMENT program works with ARC/INFO revisions 7.0.2 and 7.0.3. Although the FGDC-compliant metadata files are intended to document the public-domain-format (DLG or ASCII-tabular) files, the DOCUMENT program produces metadata files that contain some ARC/INFO-specific terminology. Users are cautioned not to be confused by this terminology. The FGDC-compliant metadata files should contain enough information to eliminate any confusion caused by the use of ARC/INFO-specific terminology.

File Formats

The data sets on this disc are stored in one of three generic or public-domain formats, depending on the type of data represented. The stream gages, reservoir gages, and meteorological stations are treated as points, and are stored in simple ASCII files, with fixed-field columns. Location is indicated by latitude and longitude, in decimal degrees, and by Cartesian (X,Y) coordinates based on the Lambert Azimuthal Equal Area map projection. The Digital Elevation Model (DEM) is stored as a raster image in I*2 integer (16 bit) format. Other data sets (vector data) may be represented as either lines or polygons on a map. These data sets are stored in Digital Line Graph (DLG) Version 3, Optional Format. Some of the data sets stored in DLG format have accompanying fixed-format ASCII files that contain attribute data related to the lines or polygons defined in the DLG file. Complete descriptions of these related data files are contained in the narrative sections of the metadata documentation files for the associated data sets. In addition to these generic or public-domain formats, each data set is provided in ARC/INFO format, because ARC/INFO was used in developing the data sets.

ASCII File format ----------------

The ASCII files are fixed record-length, fixed-field, plain text files. Most fields are separated by at least one space. Fields not completely filled are padded with spaces. A complete description of the fields for each file is in the accompanying metadata documentation file for the data set.

Raster Format -------------

The DEM is stored in a generic raster file format with name "USCANDEM.BIL" and ARC/INFO header file with name "USCANDEM.HDR". Also included is a label file named "USCANDEM.LBL", for use by the public domain IMDISP image-display software for MS-DOS personal computers developed by the Jet Propulsion Laboratory in Pasadena, California. IMDISP users can access the DEM image by selecting the label file. The program will automatically access all the necessary header information and retrieve the image data for display on the PC screen. More information about the DEM file format may be found in the documentation file "USCANDEM.DOC", which is stored in the "\TERRAIN" directory with the DEM files.

Vector Format -------------

The vector files on this disc are in the USGS Digital Line Graph, Version 3 (DLG-3) optional format. Designed for data interchange, this format allows for the simple creation of a vector 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 U.S. Geological Survey (1990).

ARC/INFO Export Format ----------------------

Each of the data sets were processed using the ARC/INFO software package, and ARC/INFO export files are provided in the "\XPORTARC" directory. The export files were created using ARC/INFO Revision 6.1.1, running on a Data General AViiON workstation. The "NONE" compression option was used with the ARC/INFO EXPORT command, then the resulting export files were compressed using the GNUZIP compression utility. The "README.TXT" file in the "\XPORTARC" directory lists the original file sizes before compression. The DEM was stored on the disc in ARC/INFO grid format, using ARC/INFO version 7.0.2.

GEOMETRIC REGISTRATION

The Lambert Azimuthal Equal Area map projection was chosen for the data sets on this disc. This projection is appropriate for maps of the North American continent because of its visual presentation and equal-area characteristic, which facilitates areal analysis. To the best knowledge of the authors and contributors, all latitudes and longitudes reported are based on the North American Datum of 1927 (NAD27), and all elevations reported are relative to the National Geodetic Vertical Datum of 1929 (NGVD29). However some latitudes and longitudes may have been based on the newer North American Datum of 1983 (NAD83). Horizontal differences may be as large as 300 meters ground distance between points having identical latitudes and longitudes based on NAD27 and NAD83. Because many data bases currently do not record datum information, it is possible that some latitudes and longitudes may be based on NAD83.

The Cartesian (X,Y) coordinate system cast on the Lambert Azimuthal Equal Area map projection matches that used for the series of Advanced Very-High Resolution Radiometer (AVHRR) satellite biweekly composite CD-ROM's (Eidenshink, 1992), the Prototype 1990 Conterminous U.S. Land Cover Characteristics Data Set (U.S. Geological Survey and Univ. of Nebraska, 1993), and several other CD-ROM data sets produced by the U.S. Geological Survey. All the data sets on this CD-ROM may be used with those data sets without coordinate transformation. Table 1 provides map projection information. The Lambert Azimuthal Equal Area projection is implemented in spherical form by the software used (Environmental Systems Research Institute, 1992). The radius of the sphere of reference is such that the sphere has the same surface area as the Clarke 1866 ellipsoid, upon which the NAD27 is based (Snyder, 1987, p. 16).

Many numerical weather models use a coordinate system based on a spherical model of the earth. The radius of the sphere used may be different from the radius used for the data sets on this disc. In addition, the Clarke 1866 ellipsoid, which was used for the basis of NAD27 and most currently available maps, was offset from a geocentered position, in order to fit North America more closely (Snyder, 1987, p. 12). Conversion of latitudes and longitudes based on differing ellipsoids or spheres may involve several steps. The documentation file for the Eta model (\ETAMODEL\ETAMODEL.DOC) contains a detailed discussion of the process used to convert the Eta-model latitudes and longitudes to coordinates that may be referenced to the other map-based data sets included on this disc.

Table 1. Lambert Azimuthal Equal Area projection
______________________________________________________________________________
Projection parameters:
Radius of sphere 6,370,997.0 meters
Longitude of center of projection 100 00 00 West
Latitude of center of projection 45 00 00 North
Coordinate system parameters:
False easting 0
False northing 0
Units of measure: meters
______________________________________________________________________________

Software

Because the global-change research community for which this CD-ROM is primarily intended is very diverse and uses a variety of computer equipment, the primary focus for this compact disc has been to provide data sets in standard, generic formats. The assumption is that the individual user will be able to integrate the data sets into his or her particular computer software and hardware environment. In general, no data-management or display software are provided. The International GEWEX office will maintain lists of sources of software packages and other data sets which may be useful with this disc.

Software is provided on this disc, however, for transforming coordinates between latitude-longitude (NAD27) and Lambert Azimuthal Equal Area coordinates. Personal-computer executable programs and C-language source code for these functions are provided in the "\SOFTWARE" directory. Also included is the entire FORTRAN source code and documentation for the General Cartographic Transformation Package (GCTP), can transform coordinates between any of the 24 map projections supported (U.S. Geological Survey, 1991).

Because some of the files have been stored on this disc in compressed form, the GZIP program also is provided in the "\SOFTWARE" directory. The GZIP program may be used to uncompress the compressed files.

Acknowledgments

Numerous people and agencies contributed data sets and time to make this disc possible. Steve Williams and Linda Cully, of the University Corporation for Atmospheric Research (UCAR), in Boulder, Colorado, compiled the non-USGS meteorological-stations data set. Terry Krauss and his colleagues, of Environment Canada, were instrumental in providing the Canadian hydrometric and climatological station catalogs without restrictions on the distribution. Richard Heim, of the National Climatic Data Center, provided the data and original maps of the Climatography of the United States. Kenneth Mitchell, National Meteorological Center, provided the Eta model grid. David Maidment, University of Texas at Austin, provided valuable consultation on coordinate conversions for the Eta model grid. Authors, contacts, and reviewers for all data sets are listed in the documentation files for the individual data sets.

References Cited

Eidenshink, J.E., 1992, The conterminous United States AVHRR data set: Photogrammetric Engineering and Remote Sensing, v.58, no.6, p. 809-813.

Environmental Systems Research Institute (ESRI), 1992, ARC Command References, Revision 6.1.1: Redlands, CA, Environmental Systems Research Institute, Inc., various pagination.

Slack, J.R., Lumb, A.M., and Landwehr, J. M., 1993, Hydro-climatic data network (HCDN) streamflow data set, 1874-1988: U.S. Geological Survey Water-Resources Investigations Report 93-4076, CD-ROM.

Snyder, J.P., 1987, Map projections--A working manual: U.S. Geological Survey Professional Paper 1395, 383 p.

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 Instruction, 70 p.

U.S. Geological Survey, 1991, General Cartographic Transformation Package (CGTP), software documentation: U.S. Geological Survey National Mapping Program Technical Instruction, 87 p.

U.S. Geological Survey and University of Nebraska, Lincoln, 1993, Prototype 1990 Conterminous U.S. land cover characteristics data set: U.S. Geological Survey, CD-ROM.

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