Which term describes the vertical distance between index contour lines?

Which term describes the vertical distance between index contour lines?

• A. Index Contour Interval
• B. Contour spacing
• C. Elevation difference
• D. Slope gradient

Answer: (A)

On a topographic map, index contours are the bolder, labeled lines that appear at regular intervals. The vertical distance from one index contour to the next is called the index contour interval. This is a specific measure that depends on how the map is set up (for example, if the standard contour interval is 20 feet and index contours are every five lines, the index contour interval is 100 feet). It differs from contour spacing, which describes how close the lines are on the map and relates to slope, and from generic elevation difference or slope gradient, which aren’t specific to the interval between index contours.