In Philippine geodesy, the Vigan Datum is best described as which of the following?

• A. Local reference datum for a region
• B. Global ellipsoid model
• C. Time standard
• D. Cartographic projection

Answer: (A)

Geodetic datum provides a fixed reference frame for positions on the Earth. When a datum is regional, it is chosen to best fit a particular area, reducing distortions in that region. The Vigan Datum is such a regional reference frame used in Philippine surveying. It defines a specific ellipsoid and origin tied to the area around Vigan, so that coordinates measured there are consistent within that region. It is not a global ellipsoid, which would apply worldwide, nor a time standard, nor a cartographic projection, which is about mapping the curved Earth to a flat plane. Therefore, the Vigan Datum is best described as a local reference datum for a region.