EPSG:4326 vs EPSG:2154 — WGS 84 vs RGF93 / Lambert-93
EPSG:4326 (WGS 84) is global longitude/latitude in degrees. EPSG:2154 (RGF93 / Lambert-93) is the official projected CRS for mainland France and Corsica: a Lambert Conformal Conic projection in meters, designed so a single grid covers the whole country with controlled distortion. Coordinates look entirely different — a Paris point is about (2.35, 48.85) in 4326 but around (652000, 6862000) meters in 2154. Lambert-93 lets you measure distances and areas directly in meters across France; WGS 84 degrees do not have a constant ground distance, so they're poor for measurement but ideal for interchange.
| Property | EPSG:4326 | EPSG:2154 |
|---|---|---|
| EPSG code | EPSG:4326 | EPSG:2154 |
| Name | WGS 84 | RGF93 / Lambert-93 |
| Type | Geographic | Projected |
| Units | degrees | metres |
| Datum | WGS 84 | RGF93 |
| Area of use | Worldwide | France – onshore and offshore, mainland and Corsica |
| proj4 | +proj=longlat +datum=WGS84 +no_defs | +proj=lcc +lat_1=49 +lat_2=44 +lat_0=46.5 +lon_0=3 +x_0=700000 +y_0=6600000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs |
When to use EPSG:4326
Use EPSG:4326 to share French data with global tools, web maps and GeoJSON consumers, or when the audience isn't France-specific.
When to use EPSG:2154
Use EPSG:2154 for official French datasets, cadastral and engineering work, and any analysis where you need to measure distance or area in meters across France. It is the IGN and government standard.
Converting between EPSG:4326 and EPSG:2154 is a reprojection, not a relabel. Convert and reproject a file or detect your CRS.
Frequently asked questions
What is EPSG:2154 used for?
EPSG:2154 (RGF93 / Lambert-93) is the official coordinate reference system for France. It's a metric projected grid used by IGN, the French cadastre, and government and engineering datasets covering mainland France and Corsica.
Why are my French coordinates six- and seven-digit numbers?
Because they're in Lambert-93 (EPSG:2154), a projected CRS measured in meters — eastings around 700000 and northings in the millions. That's expected for 2154; it is not WGS 84 degrees and must be reprojected before a degree-based tool will place it correctly.
How do I convert Lambert-93 to lat/lng?
Reproject from EPSG:2154 to EPSG:4326. This applies the inverse Lambert Conformal Conic projection plus the RGF93→WGS 84 datum step, turning meters into longitude/latitude degrees. A simple relabel won't work — the math is required.
Is RGF93 the same as WGS 84?
RGF93 (the datum behind Lambert-93) is very close to WGS 84 — within a few centimeters — because RGF93 is the French realization of ETRS89. The datums nearly coincide, but the projections differ: degrees in 4326, meters in 2154.