What is an index contour?

Answer: A — contour line that is labeled with an elevation

An index contour is a contour line that is labeled with an elevation value, which serves to provide reference points on a topographic map. These lines are typically spaced more widely apart than minor contour lines, making it easier for individuals to interpret changes in elevation. Index contours are often drawn in a darker line or different style to distinguish them from minor contour lines, which represent smaller elevation changes. By marking specific elevations, they assist in determining the steepness of terrain and navigating features of the landscape effectively. The feature of index contours helps in reading and analyzing geographical representations, as they provide clear points of reference that simplify the understanding of topography.