What Distinguishes a Topographic Map?
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. Topographic maps use a wide variety of symbols (this is an external link to the UC Berkeley Library) to represent human and physical features. (More information on map symbols is given at the USGS site, http://mac.usgs.gov/mac/isb/pubs/booklets/symbols/.) Among the most striking is the map display of the topography or terrain of the area. Contour lines are used to represent elevation by connecting points of equal elevation. These imaginary lines do a nice job of representing the terrain. When contour lines lie close together, they represent a steep slope; lines far apart represent a gradual slope. Each quad
