On a topographic map, what is an index contour line?

On a topographic map, what is an index contour line?

• A. A contour line that has a number written on it indicating elevation
• B. A dashed line indicating approximate elevation
• C. A line marking water depth
• D. A political boundary line

Answer: (A)

An index contour line is the contour line that has an elevation value written on it. On a topographic map, lines connect points of equal elevation, and the index lines are the ones you can read to know the exact height at that location. They’re placed at regular intervals and help you gauge nearby elevations and slope quickly. The other options don’t fit because a dashed line would indicate something else like an approximate line or a secondary feature, water-depth lines aren’t part of land elevation on a standard topo map, and political boundaries are unrelated to elevation contours.

An index contour line is the contour line that has an elevation value written on it. On a topographic map, lines connect points of equal elevation, and the index lines are the ones you can read to know the exact height at that location. They’re placed at regular intervals and help you gauge nearby elevations and slope quickly. The other options don’t fit because a dashed line would indicate something else like an approximate line or a secondary feature, water-depth lines aren’t part of land elevation on a standard topo map, and political boundaries are unrelated to elevation contours.