http://egsc.usgs.gov/isb/pubs/factsheets/fs08801.html
A digital raster graphic (DRG) is a scanned image of a U.S. Geological Survey topographic map. The scanned image includes all map collar information. The image inside the map neatline is georeferenced to the surface o the earth and fit to the Universal Transfer Mercator projection. The map above is a part of the Washington West, D.C. digital raster graphic.
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