What is the main purpose of contour lines on a map?

The main purpose of contour lines on a map is to represent changes in elevation. These lines connect points of equal elevation above sea level, allowing users to visualize the terrain's shape and slope. When contour lines are close together, it indicates a steep slope, while spaced-out lines suggest a gentler slope. Understanding elevation changes is crucial for various activities, such as hiking, planning construction, or assessing water runoff in a landscape.

The other options do not accurately describe the function of contour lines. Vegetation types are typically shown using different colors or symbols on a map, while population density is represented through shading or dot density. Roads and highways can be marked on a map with lines or symbols but are not indicated through contour lines, which are specifically focused on representing changes in physical elevation.