Which statement best defines a vertical datum?

Which statement best defines a vertical datum?

• A. Measures the elevations of specific points on the earth.
• B. Is a collection of specific points on the Earth with known heights either above or below mean sea level (MSL).
• C. This data is gathered via tides with sea level measurements, geodetic surveying with different ellipsoid models used with the horizontal datum, and gravity, measured with the geoid.
• D. A method used to measure atmospheric pressure at survey sites.

Answer: (B)

A vertical datum is the reference surface used to express elevations. It provides the zero-height origin and defines how all heights are measured relative to that surface, typically tied to mean sea level or a geoid. The option describing a network of specific points on the Earth with known heights above or below mean sea level matches this idea: it represents the benchmarks and their assigned elevations that establish the reference surface used for vertical measurements. The other choices describe general data collection of elevations, the methods involved in determining heights (including sea level, geoid, and ellipsoid considerations), or an entirely different measurement (atmospheric pressure), none of which define the reference surface used for vertical measurements.

A vertical datum is the reference surface used to express elevations. It provides the zero-height origin and defines how all heights are measured relative to that surface, typically tied to mean sea level or a geoid. The option describing a network of specific points on the Earth with known heights above or below mean sea level matches this idea: it represents the benchmarks and their assigned elevations that establish the reference surface used for vertical measurements. The other choices describe general data collection of elevations, the methods involved in determining heights (including sea level, geoid, and ellipsoid considerations), or an entirely different measurement (atmospheric pressure), none of which define the reference surface used for vertical measurements.