Which statement best describes horizontal datums?

• A. They are used to define positions such as latitude and longitude on the Earth's surface
• B. They determine tidal datums
• C. They measure elevations relative to MSL
• D. They classify map projections

Answer: (A)

Horizontal datums establish the reference surface used to locate points in terms of latitude and longitude on the Earth's surface. They define the reference ellipsoid and its origin, so geographic coordinates are tied to a consistent shape and starting point. Elevations and heights, on the other hand, come from vertical datums tied to mean sea level or another surface; tidal datums relate to water levels, not horizontal position; and map projections deal with flattening the curved surface for drawing, which uses a datum but isn’t what a horizontal datum itself describes. So the statement that best describes horizontal datums is that they are used to define positions such as latitude and longitude on the Earth’s surface.