DRG stands for digital raster graphics. It is a scanned image of the USGS standard series topographic map including all map collar information. The DRG can be used to collect, review, and revise other digital data, especially Digital Line Graphs. The DRG above shows the Colorado River from the USGS. Contour lines are also present and help show the topography.
http://www.tceq.texas.gov/gis/drg.html
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