Answer: A map is a representation of the Earth, or part of it. Traditionally, maps have been printed on paper. When a printed map is scanned, the computer file that is created may be called a digital raster graphic. Scanned USGS topographic maps in GeoPDF format are available for download from the USGS Store.
The distinctive characteristic of a topographic map is that the shape of the Earth's surface is shown by contour lines. Contours are imaginary lines that join points of equal elevation on the surface of the land above or below a reference surface such as mean sea level. Contours make it possible to measure the height of mountains, depths of the ocean bottom, and steepness of slopes.
A topographic map shows more than contours. The map includes symbols that represent such features as streets, buildings, streams, and woods.
|
U.S. Department of the Interior |
U.S. Geological Survey