Terrain shape and elevation.
On a topographic map, contour lines represent the shape and elevation of the land. They provide a three-dimensional perspective on a two-dimensional map by indicating the relative steepness or flatness of the terrain.
Each contour line connects points of equal elevation. For example, every point on a specific contour line might be exactly 1000 meters above sea level. The distance between contour lines indicates the slope of the terrain – if the lines are close together, it indicates a steep slope, while lines that are far apart represent a gentler slope. Closed contour lines typically indicate hilltops or depressions in the terrain.