QGIS handles coordinate reference systems (CRS) automatically in most cases. This guide covers the essentials you need to know when data looks wrong on the map.
What is CRS?
Coordinate Reference Systems in QGIS
A CRS defines how coordinates on the Earth's surface are represented. Two datasets with different CRS values will not align on the map even if they cover the same area. QGIS can reproject data on the fly, but for best performance you should reproject your data to a consistent CRS.
| CRS | EPSG code | Use when |
|---|---|---|
| WGS 84 | EPSG:4326 | Global, GPS data, lat/lon coordinates |
| Web Mercator | EPSG:3857 | Web maps, basemaps (OpenStreetMap) |
| British National Grid | EPSG:27700 | UK data |
| UTM zones | EPSG:326xx | Regional metric work |
| ETRS89 | EPSG:4258 | European datasets |
Set project CRS
Set the project CRS in QGIS
- 1
Open project properties
Project → Properties → CRS tab. Or click the CRS indicator in the status bar at the bottom right.
- 2
Search for your CRS
Type the EPSG code (e.g.
4326) or the CRS name. Select from the results and click OK. - 3
Enable on-the-fly reprojection
QGIS enables on-the-fly reprojection automatically — layers with different CRS are reprojected to the project CRS for display. This is enabled by default.
Reproject data
Permanently reproject a layer
For best performance, reproject your data to the project CRS rather than relying on on-the-fly reprojection:
# In QGIS: Vector > Data Management Tools > Reproject Layer
# Or via command line:
C:\OSGeo4W> ogr2ogr -t_srs EPSG:27700 output_BNG.gpkg input_WGS84.gpkg
# For rasters:
C:\OSGeo4W> gdalwarp -t_srs EPSG:27700 input.tif output_BNG.tif
FAQ
CRS questions
My layers are not aligning on the map
The layers have different CRS values. Check each layer's CRS: right-click layer → Properties → Source tab. If they differ, either set the project CRS to match the majority of your data and let QGIS reproject on the fly, or permanently reproject the mismatched layers.
Layer appears in the wrong location (far from expected)
The layer probably has no CRS set or has been assigned the wrong CRS. Right-click the layer → Set CRS → Set Layer CRS, and choose the correct CRS for that data. Do not reproject — just assign the correct CRS.
How do I find the EPSG code for my country?
Search at epsg.io by country name or CRS name. In QGIS, you can also check the CRS selector and browse by region.