A DRG Map, or Digital Raster Graphic Map, uses the U.S. Geological Survey standard series. It is a scanned image of this USGS topographic series which includes all map collar information. The image is georeferenced to the surface of the Earth according to the Mercator projection. Therefore, the image matches the accuracy and datum of the source map. These maps, such as the ones below are particularly useful because they are accurate to the common Mercator projection scale, and at the same time, employ precise satellite imaging techniques.
http://topomaps.usgs.gov/drg/
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