Getting USGS Data

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USGS QuadsQuad Names

Arc vs. Meters

Arc Meters (approximate) Used for
1 degree 110 kilometers  
7.5 arc minutes 14 kilometers Size of a traditional map "quad"
30 arc seconds 1 kilometer Global elevation
3 arc seconds 90 meters World-wide SRTM
1 arc second 30 meters DEM from topo, USA SRTM
1/3 arc second 10 meters DEM from topo
1/9 arc second 3.4 meters Newer DEM from LIDAR