DRG

A DRG, or also known as a digital raster graphics, map is a scanned image of a U. S. Geological Survey standard series topographic map. DRG's are used as the basis for the USGS DLG files and DEM files. They are usually scanned at 250 dpi. This DRG is of the entire U.S..

http://www.drgmaps.com/map.gif