Most USGS topographic maps use contours to show the shape and elevation of the terrain. Elevations are usually shown in feet, but on some maps they are in meters.
Contour intervals vary, depending mainly on the scale of the map and the type of terrain.
The DRG data are being produced by the USGS through an Innovative Partnership agreement with The Land Information Technology Company, Ltd., of Aurora, Colorado. This series includes DRGs of USGS standard series quadrangle maps of the United States, its Trusts, and Territories. The standard area of coverage of a DRG is the entire area printed on a USGS standard series topographic map including the map collar, any overedge areas, and insets. The image inside the map neatline is georeferenced and fit to the Universal Transverse Mercator projection. The horizontal positional accuracy and datum of the DRG matches the accuracy and datum of the source map.