Which term describes the height above the geoid measured along the local vertical?

• A. Orthometric height
• B. Ellipsoidal height
• C. Geoid height
• D. Geodetic height

Answer: (A)

Height above the geoid measured along the local vertical is orthometric height. This quantity uses the geoid, which mirrors mean sea level, as the reference surface, and follows the direction of gravity (the plumb line) from the geoid up to the point on the Earth’s surface. In contrast, ellipsoidal height is measured along a line normal to the reference ellipsoid, not along the gravity vector, and geoid height describes how far the geoid is above or below the ellipsoid. Geodetic height is a broader term that often corresponds to height relative to the ellipsoid in many contexts.