The default coordinate system is Web Mercator (EPSG:3857).
For more information, see the article on System installation parameters.
Advantages of Web Mercator
- Web Mercator is used by most online map services (Google Maps, OpenStreetMap). It is the standard.
- Modern tools and software libraries for building online maps are optimised for this layout, which makes the map work the fastest.
- This layout is suitable for the entire world
Disadvantages of Web Mercator
- It is a worldwide layout, which means that its accuracy is not geodetic. This means that measurement inaccuracies are significant.
- Not all national spatial data services (e.g. WMS from Geoportal.gov.pl) are published in this layout, so reprojection is necessary, which takes time and may affect the quality of the WMS data.
- This is not the optimal layout for use on map printouts, for several reasons.
- Distortion: EPSG:3857 is a Mercator (Web Mercator) datum, which significantly distorts areas, especially at high latitudes (north and south). On a map in the Mercator system, areas close to the poles appear much larger than they actually are, which can lead to misinterpretations of the data.
- Scale: Because of this distortion, the scale on the EPSG:3857 map is not constant, which can be problematic for map printouts. For a web map, where the user can zoom in and out, the scale is less important, but on a printed map, the scale should be constant.
- Units: EPSG:3857 uses metres as a unit, but due to distortion, these metres are not ‘real’ metres on the Earth’s surface, especially near the poles.
What are the alternatives?
If the data displayed in the System is to be applicable to Poland, it is possible to install the application in the PUWG 1992 system (EPSG:2180), but to optimise the display of the data in a web browser, the map will be displayed in Web Mercator (EPSG:3857).