[coordinate systems]
A set of parameters that define the coordinate system and spatial properties for geographic data. A spatial reference is used to provide a framework when measuring and representing geographic features from different sources. Each spatial reference is defined either by a WKID—also called a spatial reference ID (SRID)—or by a WKT. Common spatial references include WGS84, used by GPS systems, and web Mercator projections, used in most web maps.