For vertical/elevation heights, to which datum should the geodetic datum be referenced?

For vertical/elevation heights, to which datum should the geodetic datum be referenced?

• A. Mean sea level globally.
• B. Global ellipsoid datum.
• C. NAD 83 datum.
• D. Local benchmark datum.

Answer: (D)

Vertical/elevation heights are defined relative to a vertical datum, a reference surface for heights. That surface isn’t the global mean sea level or a global ellipsoid, and it isn’t a horizontal datum like NAD 83. Instead, elevations are tied to a local benchmark datum that’s realized through a regional leveling network and local tide/sea-level measurements. This local vertical datum provides a stable, consistent reference for heights within the area of interest, ensuring surveyed elevations align with the local control. Global mean sea level varies by location and time, and a global ellipsoid serves horizontal positioning, not heights, while NAD 83 is a horizontal datum. Therefore, the appropriate reference for vertical/elevation heights is the local benchmark datum.

Vertical/elevation heights are defined relative to a vertical datum, a reference surface for heights. That surface isn’t the global mean sea level or a global ellipsoid, and it isn’t a horizontal datum like NAD 83. Instead, elevations are tied to a local benchmark datum that’s realized through a regional leveling network and local tide/sea-level measurements. This local vertical datum provides a stable, consistent reference for heights within the area of interest, ensuring surveyed elevations align with the local control. Global mean sea level varies by location and time, and a global ellipsoid serves horizontal positioning, not heights, while NAD 83 is a horizontal datum. Therefore, the appropriate reference for vertical/elevation heights is the local benchmark datum.