What does the term "datum" refer to in GIS?

In the context of Geographic Information Systems (GIS), the term "datum" refers to a reference point for measurements, which is critical for defining geographic locations accurately. A datum provides the foundational framework that allows for consistent and reliable measurements on the Earth's surface.

Specifically, a datum includes both a reference surface, such as an ellipsoid or geoid, and a set of parameters that help to describe the position of the ellipsoid relative to the center of the Earth. This ensures that coordinates for locations on the Earth's surface can be standardized, which is essential for mapping and spatial analysis.

The other choices do not fully encapsulate the definition of "datum" in GIS. Theoretical lines of latitude and longitude are components associated with geographic coordinate systems, but they do not encompass the broader meaning of a datum itself. Spatial analysis refers to analytical techniques used in GIS, rather than the reference frameworks of a datum. A coordinate system, while related, is a more extensive concept that includes various datums, spatial references, and projections but does not specifically denote the reference point aspect that a datum represents.