A map is a representation of the earth, or part of it. The distinctive characteristic of a topographic map is the use of contour lines to show the shape of the earth's surface. USGS topographic maps also show many other kinds of geographic features, including roads, railroads, rivers, streams, lakes, buildings, built-up areas, boundaries, place or feature names, mountains, elevations, survey control points, vegetation types, and much more.
So, what exactly is a contour line? Contours are lines drawn on a map that join points of equal height. Contours make it possible to show the height and shape of mountains, depths of the ocean bottom, and steepness of slopes. Basically, 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.
Topographic Maps Symbols
Historical USGS Topographic Maps
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