Which statement describes a geocentric datum?

• A. A geocentric datum uses a region-specific origin with local orientation.
• B. A geocentric datum is based on mean sea level.
• C. A geocentric datum uses the Earth's center as origin with a global orientation.
• D. A geocentric datum uses a tidal datum.

Answer: (C)

Geocentric datums place the origin at the Earth's center of mass and use a global, Earth-fixed orientation for the coordinate axes. This creates a single, worldwide reference frame that works for GPS and global mapping, since every position is expressed relative to the same central point and fixed directions. In contrast, regional datums have origins tied to specific local points with local orientation, vertical or tide-based references relate to heights or sea surface levels rather than horizontal coordinates, and tidal datums describe sea surface levels, not a global 3D frame. So using the Earth's center as origin with a global orientation best captures what a geocentric datum is.