How do topographic maps describe the terrain?
Topo maps describe the physical shape of the land using contour lines. These lines describe three-dimensional features by outlining them at specific elevation intervals (every 10, 20 or 50 feet, for example, depending upon the map being used). The vertical difference between any two adjacent contour lines is always the same throughout a given map. This distance, called the contour interval, is identified at the bottom of each map. Every fifth contour line is called an index contour line. Index contour lines have numeric elevations (usually measured in feet above sea level) printed on them that show how high all points along that line are. Using the numeric information from the index contours and the interval information from the bottom of the map, you can figure out: • How high your current position is (assuming you know where you are on your map) • How high any other specific point on the map is • How steep the terrain is between where you are and where you want to go The steepness of
