What datum is used on USGS DRG files?
USGS DRG topo map files tend to use the NAD27 datum, the same as that used on the actual paper maps. Note that if you use coordinates read off a topographic map with your GPS, you may want to make sure you’re using the same datum as the map. Most GPS’s default to NAD83 (or WGS84, which is the same) datum. You can change the datum of the coordinates displayed in the Map Viewer by selecting the desired datum from the sidebar.
