A level datum is defined as which?

• A. An arbitrary level surface to which elevations are referred; mean sea level is a common example.
• B. The true geoid used as Earth's gravity surface.
• C. The average elevation of all points in a project.
• D. The elevation of the highest benchmark.

Answer: (D)

A level datum is a reference surface used to express elevations consistently. It isn’t a single point, but a fixed surface that elevations are measured from, so all heights in a project share the same baseline. In practice mean sea level is a common example because it represents the average height of the ocean’s surface over time, serving as a practical reference for land elevation. The geoid is a related concept—it’s an equipotential surface of Earth’s gravity field that closely matches mean sea level globally, and some datums use this surface as their reference. Elevations tied to a datum are measured relative to that surface, not to the highest benchmark or to the average of all points in the project.