DRG

A digital raster graphic (DRG) is a scanned image of a U.S. Geological Survey (USGS) standard series topographic map, including all map collar information. The image inside the map neatline is georeferenced to the surface of the earth and fit to the Universal Transverse Mercator projection. This DRG is a map of a section of Michigan.

http://lter.kbs.msu.edu/maps/GIS/DRG_d.jpg