Which of the following is not a part of a geographic coordinate system?

• A. Angular units
• B. Datum
• C. Planisphere
• D. Prime Meridian

Answer: (C)

A geographic coordinate system is defined by how we measure location on the Earth using angles, a reference frame, and a reference longitude. Angular units (degrees, minutes, seconds) are used to express positions on the spherical surface. A datum provides the reference shape and size of the Earth and anchors coordinates to a real model. The Prime Meridian establishes the 0° longitude from which east and west are measured. A planisphere, on the other hand, is a star chart or a device for locating celestial objects, not a component that defines or references positions on the Earth. So the item that doesn’t fit as part of a geographic coordinate system is the planisphere.