Contour lines are lines drawn on a topographic map to indicate ground elevation or depression. They mark points of equal elevation on a map, and if you trace the length of a line with your finger, each point you touch is the same height above sea level. The vertical distance or difference in elevation between contour lines is called the contour interval.

Contour lines are critical to understanding the elevation profile of your terrain or a particular land formation. They show the shape of the land, including mountains, valleys, and plains, by means of brown contour lines (lines of equal elevation above sea level) . The less separation between contour lines, the steeper the slope, and the more widely separated they are, the gentler the slope.

Contour lines also indicate the shape of the terrain. Roughly concentric circles are probably showing you a peak, and areas between peaks are passes. Studying a topo map of a familiar area is a great way to learn how to match terrain features with the contour lines on a map.

In summary, contour lines represent ground elevation or depression on a topographic map. They mark points of equal elevation and show the shape of the land, including mountains, valleys, and plains. The less separation between contour lines, the steeper the slope, and the more widely separated they are, the gentler the slope.