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9 February 2026*A description in non-technical language
A coordinate system describes how location data for objects on the Earth’s surface (which is roughly spherical) is transformed onto a map (which is flat—both paper maps and maps displayed on a screen). Any attempt to “flatten” the surface of a sphere onto a flat map introduces distortions (in distance, area, or shape). Coordinate systems were created to minimize these distortions, depending on the area being mapped and the scale at which it is shown.
There are several thousand coordinate systems:
- Some are designed for the entire world (but they are less accurate and maps may be distorted), for example the system known as Web Mercator (EPSG:3857).
- Others apply to small areas but have very small distortions (for example, the Polish series of coordinate systems known as PUWG 2000).
The most popular uniform coordinate system for the whole of Poland is the 1992 system (EPSG:2180).
What should you remember?
- This is not a major issue for modern GIS users.
- Every map (whether on a computer or on paper) has its own coordinate system.
- Spatial data stored in appropriate files (for example, Shapefile or KML) have their own coordinate system, which can be checked in software like QGIS.
- A map on a computer can be displayed in one coordinate system, while a file may store data in another. When viewing, a process called “on-the-fly reprojection” occurs.
- Each coordinate system has its own EPSG code, which makes it easy to identify. List of EPSG codes
- A good practice is to keep data in a single coordinate system (if the nature of the data allows it).