What does a datum provide in surveying?

A datum in surveying serves as a fundamental reference point or surface utilized for measuring elevations and distances. It establishes a baseline from which all measurements are made, creating a consistent framework that enables surveyors to determine the relative heights and positions of points on the Earth's surface.

When surveyors refer to a vertical datum, they typically mean a standardized height reference system, such as Mean Sea Level, which provides a reliable surface for measuring elevation. Similarly, horizontal datums are used as reference points for mapping and detailing distances across the land. By setting a specific reference for both vertical and horizontal measurements, a datum ensures precision and uniformity in survey results.

The other options relate to different functions in land management and surveying, but they do not encapsulate the core purpose of a datum, which is to provide a reliable reference for all measurements.