Height is the distance measured along a _____ between a point on the earth's surface and a reference surface.

• A. parallel
• B. skew line
• C. curve
• D. perpendicular

Answer: (D)

Height is the vertical distance from a point on the Earth’s surface to a reference surface measured along a line that is perpendicular to that reference surface. This means the measurement follows the local vertical, or the normal to the surface, so the path meets the reference surface at a right angle. The reference surface could be the reference ellipsoid for ellipsoidal height or the geoid for orthometric height. Measuring along any line parallel to the surface would not yield a vertical distance, and lines described as skew or curved don’t define a single perpendicular path for this purpose.