Why do contours have numbers on a topographic map?

Contours on a topographic map are labeled with numbers to indicate elevation above a specific reference point, usually sea level. Each contour line connects points of equal elevation, helping users visualize the terrain's shape and steepness. The difference in elevation between adjacent contour lines, known as the contour interval, provides insight into the gradient of the landscape. This information is crucial for navigation, land use planning, and understanding geographic features.