# How to Read a Topographic Map

By: Debra Ronca  |

## Topographic Map Contour Lines

Co­ntour li­nes are the greatest distinguishing feature of a topographic map. Contour lines are lines drawn on a map connecting points of equal elevation, meaning if you physically followed a contour line, elevation would remain constant. Contour lines show elevation and the shape of the terrain. They're useful because they illustrate the shape of the land surface — its topography — on the map. Here's a cool way to understand how to interpret contour lines: Take an object like a ball or a pile of laundry, and shine a red laser pointer along the object's side. The line you see will look like a contour line on a topographic map.

In order to keep things simple, topographic maps show lines for certain elevations only. These lines are evenly spaced apart. We call this spacing the contour interval. For example, if your map uses a 10-foot contour interval, you will see contour lines for every 10 feet (3 meters) of elevation — lines at 0, 10, 20, 30, 40 and so on. Different maps use different intervals, depending on the topography. If, for example, the general terrain is quite elevated, the map might run at 80- to even 100-foot (24- to 30-meter) intervals. This makes it easier to read the map — too many contour lines would be difficult to work with. Look in the margin of your map to find out its contour interval.