Coordinate reference systems define how a given coordinate reference is related to a Location on the Earth. Because of the Earth’s complex shape, continental drift, and long history of mapping, there are literally thousands of different coordinate reference systems (CRS). Fortunately, you will normally only need to deal with a small number of CRSs depending on where and at what scale you are working (Shortlist of Danish, European and Global CRS). It is common to distinguish between two families of coordinate reference systems (CRS), namely:
- Geographic
- Projected Some typical CRSs are:
If you are creating maps over larger areas, one aspect of the CRS that needs to be taken into account is the projection
When working with z data (3D), the CRS also needs to define the baseline (sea level) for this. In this case, we talk about vertical datum.