What is the primary purpose of contour lines on a topographic map?

Contour lines on a topographic map serve to show relief and elevation, which is their primary purpose. These lines connect points of equal elevation and provide a visual representation of the terrain's shape and steepness. By analyzing the spacing of the contour lines, one can determine whether an area is flat, rolling, or steep, as closely spaced lines indicate steep slopes and widely spaced lines suggest gentler slopes. This information is crucial for various applications, including land navigation, planning construction projects, and understanding natural landscapes.