The National Geodetic Vertical Datum of 1929 is a reference for vertical positions relative to what?

The National Geodetic Vertical Datum of 1929 is a reference for vertical positions relative to what?

• A. Sea level
• B. Mean sea level
• C. Ground level
• D. Air pressure

Answer: (A)

Vertical positions are defined relative to a fixed reference surface, not to the local ground or to atmospheric conditions. The National Geodetic Vertical Datum of 1929 establishes elevations using a surface that follows the sea’s level, effectively tying height measurements to mean sea level observed across a network of tide gauges. This means land elevations are expressed as how far above that sea-level surface they sit. That’s why the reference is described as sea level. Ground level would vary with local terrain, and air pressure has no role in defining a vertical datum.

Vertical positions are defined relative to a fixed reference surface, not to the local ground or to atmospheric conditions. The National Geodetic Vertical Datum of 1929 establishes elevations using a surface that follows the sea’s level, effectively tying height measurements to mean sea level observed across a network of tide gauges. This means land elevations are expressed as how far above that sea-level surface they sit. That’s why the reference is described as sea level. Ground level would vary with local terrain, and air pressure has no role in defining a vertical datum.