Coordinate Systems Explained: WGS84, UTM and Why Your Data Doesn't Line Up

Have you ever loaded two datasets into a map and found them hundreds of metres – or kilometres – apart? The cause is almost always the coordinate reference system (CRS).

Geographic vs. projected coordinates

• Geographic coordinates use latitude and longitude in degrees on the curved Earth. Example: WGS84 (EPSG:4326), used by GPS.
• Projected coordinates flatten the Earth onto a plane and use metres. Example: UTM zones.

Projected systems are better for measuring distances and areas; geographic systems for global data exchange.

Systems common in Germany

• ETRS89 / UTM zone 32N (EPSG:25832) – the standard for official geodata in most of Germany
• ETRS89 / UTM zone 33N (EPSG:25833) – used in eastern parts
• Gauss-Krüger – an older system still found in legacy data
• Web Mercator (EPSG:3857) – used by most web maps for display

EPSG codes

Every CRS has an identifier, the EPSG code. Always store it with your data, for example in the GeoPackage or shapefile's .prj file.

Why data doesn't line up

• The data's CRS is missing or wrong
• Coordinates were copied without noting the system
• An older datum (for example DHDN) was used without proper transformation
• Latitude and longitude were swapped

How to fix it

1. Identify the correct CRS (metadata, source, typical coordinate values).
2. Assign it correctly (don't confuse "assign" and "transform").
3. Transform to a common CRS for analysis.
4. Use precise transformation grids for older German systems where accuracy matters.

Best practices

• Store data in one consistent CRS
• Document the CRS in metadata
• Use metric projected systems for analysis in Germany
• Convert to Web Mercator only for display

Getting coordinates right is a basic but essential part of every GIS project – and something we check first when integrating data.