DRG

http://www.tceq.texas.gov/gis/drg.html

Known as a Digital Raster Graphic, a DRG map is an image of a topographic map provided by the USGS that has been scanned through a computer.  These maps provide a multitude of information such as geographical features, spacial data, etc.  The map provided is a scanned topographic map that is showing the Colorado River within an urban area.  The different amounts of information such as highlighted streets make this map a DRG map.