On a topographic map, what do contour lines represent?

Contour lines on a topographic map represent elevation changes and are used to illustrate the three-dimensional shape of the terrain on a two-dimensional surface. Each contour line connects points of equal elevation above a specified reference, usually sea level.

The spacing of these lines is significant; closely spaced lines indicate a steep slope, while widely spaced lines suggest a gentle slope. Understanding how to read contour lines is crucial for understanding the topography of an area, including hills, valleys, and plateaus, allowing one to visualize the landscape's elevation changes effectively.

Options addressing water bodies, vegetation types, and roads do not pertain to the fundamental purpose of contour lines, which is strictly about representing elevation. Therefore, B is the only accurate choice in this context.