A DRG (digital raster graphic) is a scanned image of a U.S. geological survey topographic map. Typically USGS 7.5-minute quadrangle are the images that are scanned for DRG, but can include any raster graphic as long as it is georeferenced so the images could interlay with one another. The picture above is a DRG showing the western section of Washigton, D.C.
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