Coordinate reference systems are used to project the three-dimensional Earth onto two-dimensional maps. There are many such models for expressing locations on Earth in a coordinate system. Spotfire supports more than 3,000 of them, but the geocoding data tables provided by Spotfire are expressed in the coordinate reference system EPSG:4326-WGS84, which we will use for all the geographic examples in this chapter. You don't need a coordinate reference system for plotting and layering data on two-dimensional images.