What is the standard vertical reference point usually used in surveying?

The standard vertical reference point commonly utilized in surveying is mean sea level. This reference point is established as a baseline for measuring elevations and depths on the Earth's surface. Mean sea level is derived from averaging the sea levels over a period of time, accounting for factors such as tides, atmospheric pressure, and other influences.

Using mean sea level as a reference point provides a consistent and universally accepted baseline for engineers and surveyors to accurately determine the relative heights of various features, ensuring that all measurements can be compared and interpreted uniformly. This is particularly important in large-scale construction projects and in the creation of maps or geographic information systems (GIS).

Other options such as mean high tide or average land elevation do not serve as standardized references for elevation measurements across different locations as effectively as mean sea level does. Ground level, while relevant for specific projects or local surveys, can vary significantly from one site to another and does not provide a consistent vertical reference.