What does a contour line indicate on a topographic map?

A contour line on a topographic map is a crucial feature that represents points of equal elevation above a specific reference point, typically sea level. By connecting these points, contour lines illustrate the terrain's shape and slope. When the lines are close together, they indicate a steep gradient, while lines that are spaced farther apart suggest a gentle slope. Additionally, if a contour line forms a closed loop that is unbroken, it may signify a hill or a depression, depending on whether the elevation increases or decreases as you move along the line.

Understanding contour lines is essential for interpreting topographic maps effectively because they provide a visual representation of the earth's elevation changes, which is vital for various applications, including land use planning, civil engineering, and outdoor activities such as hiking and camping. Therefore, a contour line is fundamentally tied to ground elevation or depression, making this option the most accurate answer in the context of the question.