DRG
Digital Raster Graphic -- is a scanned (250 dpi) topographic
map of a US Geological Survey (USGS) topographic map including all collar
information. The image inside the map neatline is georeferenced to the surface
of the earth. The majority (over 95%) of DRGs with collars are in a UTM NAD 27
(Zone varies depending upon location), However there are a small amount in NAD
83.
http://www.mapmart.com/Products/TopographicalMaps/USGSDRG.aspx
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