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)

Understanding how elevation is represented on maps hinges on index contour interval. On topographic maps, contour lines join points of equal elevation, and the index contours are the bolder lines shown at regular intervals. The vertical distance from one index contour to the next—the elevation difference between those bold lines—is the index contour interval. It reflects a fixed elevation change and is usually several regular contour intervals apart (for example, if the regular contour interval is 20 ft, index contours might be 100 ft apart). This differs from contour spacing, which is the horizontal distance between lines on the ground, and from elevation difference in general, which can refer to any change in height between two points. Slope gradient involves both vertical and horizontal change, not the spacing of index lines.

Understanding how elevation is represented on maps hinges on index contour interval. On topographic maps, contour lines join points of equal elevation, and the index contours are the bolder lines shown at regular intervals. The vertical distance from one index contour to the next—the elevation difference between those bold lines—is the index contour interval. It reflects a fixed elevation change and is usually several regular contour intervals apart (for example, if the regular contour interval is 20 ft, index contours might be 100 ft apart). This differs from contour spacing, which is the horizontal distance between lines on the ground, and from elevation difference in general, which can refer to any change in height between two points. Slope gradient involves both vertical and horizontal change, not the spacing of index lines.