Answer: A map is a representation of the Earth, or part of it. The distinctive characteristic of a topographic map is that the shape of the Earth's surface is shown by contour lines. So, what exactly is a contour line? Contours are imaginary lines drawn on a map that join points of equal height.
Imagine walking along the beach. As you walk across the sand on the shore, your elevation stays constant. That path is drawn by one contour line. Now imagine walking from the shoreline into the ocean where the ground is below sea level. That path, which follows a different elevation than when you were walking on the shore, is drawn by a different contour line.
The distinctive characteristic of a topographic map is that the shape of the Earth's surface is shown by contour lines. These imaginary lines join points of equal elevation on the surface of the land above or below a reference surface such as mean sea level.
This can help measure depths of the ocean bottom, the height of mountains, and the steepness of slopes. But topographic maps show more than contours. These maps also include symbols that represent features such as streets, buildings, streams, and woods.
Scanned USGS topographic maps in GeoPDF format are available for download from the USGS Store.
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U.S. Department of the Interior |
U.S. Geological Survey