In which coordinate system is the map displayed?

The default coordinate system is Web Mercator (EPSG:3857)

Advantages of Web Mercator

1. Web Mercator is used by most online mapping services (Google Maps, OpenStreetMap). It is the standard.
2. Modern tools and programming libraries for building online maps are optimized for this coordinate system, which ensures the fastest map performance.
3. It is a coordinate system suitable for global coverage.

Disadvantages of Web Mercator

1. It is a coordinate system suitable for the entire world, which means its accuracy is not geodetic. This results in significant measurement inaccuracies
2. Not all national spatial data services (e.g., WMS from Geoportal.gov.pl) are published in this coordinate system, so reprojection is required, which takes time and may affect the quality of WMS data.
3. It is not the optimal coordinate system for map printing, for several reasons.
   1. Distortion: EPSG:3857 is a Mercator reference system (Web Mercator) that significantly distorts areas, especially at high latitudes (near the poles). On a Mercator map, regions close to the poles appear much larger than they actually are, which can lead to misinterpretation of the data.
   2. Scale: Due to this distortion, the scale on an EPSG:3857 map is not constant, which can be problematic for printed maps. For an online map, where users can zoom in and out, scale is less critical, but for printed maps, the scale should remain consistent.
   3. Units: EPSG:3857 uses meters as its unit, but due to distortions, these meters are not “true” meters on the Earth’s surface, especially near the poles.

What are the alternatives?

If the data displayed in the system concerns Poland, it is possible to install the application using the PUWG 1992 coordinate system (EPSG:2180). However, to optimize data display in a web browser, the map will be shown in Web Mercator (EPSG:3857).