The term "contour interval" refers to the vertical distance between contiguous contour lines in terms of elevation. Commonly illustrated on a topographic map, the elevations between contour lines are uniformly spaced along vertical distances.
In cartography, a topographic map is a precise visual representation of various geographical features of a planet, which may include urban and rural areas, landforms, bodies of water or international boundaries. The contour interval varies on certain maps. In areas where there are significant changes in elevation over long distances, such as mountains and valleys, larger values are used for the contour interval. In most geological surveys conducted by the United States, the commonly used contour interval is 20 feet for a 1:24,000 map scale.