A coordinate system is an indication of how the location data of objects from the Earth’s surface (which is more or less a sphere) has been reproduced on a map (which is flat – both the paper one and the one on the screen)
There are several thousand coordinate systems:
- Some are adapted for the whole world (but are less accurate and maps can have distortions). For example, the so-called Web Mercator system (EPSG:3857)
- Others are for small areas but have very little distortion (e.g. the Polish series of layouts called PUWG 2000).
What needs to be remembered?
- It is not a big problem for modern GIS users.
- Every map (the one on the computer and the one on paper) has its own coordinate system.
- Spatial data stored in appropriate files (e.g. Shapefile or KML) has its own coordinate system (which system it is, you can check it e.g. in QGIS)
- The map on the computer may display in one coordinate system and the file may store data in another. During display, so-called on-the-fly reprojection takes place.
- Each layout has its own EPSG code so that they can be easily identified. List of ESPG codes
Article on coordinate systems