Land surveying in France: Lambert 93, RGF93 and the nine CC zones
France looks like a one-projection country; in practice one national system and nine regional zones live together.
Field takeaways
- The official datum is RGF93; the national projection is Lambert 93 (EPSG 2154).
- Nine conic Lambert CC zones are defined for large-scale work.
- Older plans sit in NTF-datum Lambert zones; no comparison without transformation.
- Lambert 93 coordinates are recognisable by seven-digit northings.
- The app opens in France with the official system covering the location.
The national frame: RGF93 and Lambert 93
France's official datum is RGF93 and the national projection is Lambert 93 (EPSG 2154). One conic projection covers the whole mainland; national datasets and many official deliveries live in this frame.
What the nine CC zones are for
The price of covering a large country with one projection is scale distortion. For large-scale work France defines nine conic zones (CC42 through CC50), each covering a latitude band and keeping distortion locally small. Cadastre and utility files can arrive in a CC zone; opening one as Lambert 93 shifts the map by hundreds of kilometres.
NTF: the old datum
Before RGF93, France used the NTF datum with the old Lambert zones. A substantial share of archived plans still sits there. The NTF-RGF93 gap is metre-level and does not close without a transformation.
What the app does in France
MapLab Survey opens in France with the official system covering the location. Lambert 93, RGF93 and the national networks sit together in the catalogue; you can bring in an old plan, compare it with the current measurement and export the delivery in the requested frame as DXF or CSV.
The recognition hint
A seven-digit northing starting with 6 is very likely Lambert 93; an eight-digit northing points at the CC zones. The only certain way remains the question: which system, which zone?
Try these steps on your own phone.
MapLab Survey handles RTK/GNSS point capture, drawing, area and volume calculations and coordinate conversion, then exports to DXF, KML/KMZ, GeoJSON, Shapefile, GeoPackage, NCZ or CSV. Capture, calculation and export work offline. Live NTRIP corrections and online basemaps need a connection.
Frequently asked questions
Which system is official in France?
Lambert 93 on the RGF93 datum (EPSG 2154); large-scale work also uses the nine Lambert CC zones.
What happens if I confuse a CC zone with Lambert 93?
The map shifts by hundreds of kilometres; the two projections use different number ranges. The digit count of the northing is the first hint.
Can I compare an old NTF plan with today's measurement?
Only through a transformation. The NTF-RGF93 gap is metre-level.
Which system does the app open with in France?
The official system covering the location; the catalogue lets you switch frames.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: Coordinate conversion app · Placing a scanned sheet · Bluetooth RTK GNSS · MapLab Survey