DRG

DRGs or Digital Raster Graphics, is a GIS creation using a topographic map and digitializing it at a very precise rate, the standard being 250 dpi. When digitalized, the map can recieve further enhancements, such as the example below, wher the map has been given simulated elevation to help further its understanding.




Found - http://pubs.usgs.gov/of/2003/of03-471/graphics/omeara/fig3.jpg