The University of Texas at Dallas
Program in Geospatial Information Sciences
USGS Digital Raster Graphs for North Texas
Location: ftp://charlotte.utdallas.edu/gisdata/UsgsDRG Also available via drive mappings in Green Hall labs.
Overview
As
originally published by the USGS, the
Digital Raster Graphic (DRG) is a raster image of a
The DRGs for North Texas have been modified by the Bruton Center for Development Studies, University of Texas at Dallas, to remove the collar information (to allow seamless mosaicing of images) and projection to State Plane Coordinate System, North Central Texas Zone, units feet. Note that not all DRGs for North Texas have been so processed. ER Mapper software was used to process the data and control files in ER Mapper format (e.g. .ers) are included in some cases.
A
DRG is useful as a source or background layer in a GIS as a means to perform
quality assurance on other digital products and as a source for the
collection and revision of DLG data. DRG's
The DRG files were published around 1997 but the scanned maps they contain are usually dated much earlier.
Tile Structure
Since they are derived from the 7.5 minute USGS quads the DRGs are organized by quadrangle name. The folder Index contains indices (in .tif image format) to the names of the individual quadrangles. USGS 7.5 minute quadrangles are published in paper format at a scale of 1:24000 (1"=2,000 feet)
The folder Quads_NCTexas_250K contains a single file (NCTexas.bil) based on USGS 1:250,000 scale mapping covering the entire North Texas area. This is also useful to help identify specific quadrangles.
File Formats
The data is available in three formats, although not all files are in all formats:
Quads_UTM_tif: The original USGS format. Data is projected to UTM and includes collars.
Quads_SPCS_bil: Data is projected to SPCS, North Central Texas Zone, feet, with collars removed. .bil format is a common format supported by many raster oriented GIS packages. It results in extremely large file size. This folder also includes some larger scale data at 1:100,000
Quads_SPCS_jpg: Data is projected to SPCS, North Central Texas Zone, feet, with collars removed. .jpg format provides smaller file sizes
Metadata
Formal FGDC compliant meta data is available for both the original USGS data and the UT-Dallas processed data in the folders: MetadataUSGS and MetadataUTD. Note that each of the files in these folders repeats the same basic information for each quadrangle. They are in text format.
Program in Geospatial Information Sciences
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University of Texas at Dallas
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