The most reliable source of elevation on a topographic map is

• A. Bench mark
• B. Contour line
• C. Scale bar
• D. Contour interval

Answer: (A)

Elevation values on a topographic map come from ground surveys anchored to fixed reference points. The benchmark is a permanently marked, precisely surveyed point with a published elevation above a standard datum. Because its height is known and does not change, it provides the true, absolute elevation reference for the map. Contour lines show areas of equal elevation and are spaced to illustrate relief; they are derived from survey data and interpolate between known elevations, so they convey relative height changes but not an exact height unless tied to a benchmark. The scale bar merely shows map distance, not elevation, and the contour interval is the vertical spacing between lines, not an absolute elevation. Therefore, the most reliable source of elevation is the benchmark.