EPSG:4326 vs EPSG:3857 — WGS 84 vs Web Mercator
EPSG:4326 (WGS 84) stores positions as longitude and latitude in degrees on the globe — it is the CRS of GPS, GeoJSON and almost all data interchange. EPSG:3857 (Web Mercator) projects those same positions onto a flat square in meters so they can be sliced into the 256×256 tiles that Google Maps, Mapbox, OpenStreetMap and Leaflet render. They share the WGS 84 datum, so the underlying positions match — but the numbers are completely different: degrees in 4326, meters in 3857. Web Mercator also distorts area badly toward the poles (Greenland looks the size of Africa) and is clipped at roughly ±85° latitude.
| Property | EPSG:4326 | EPSG:3857 |
|---|---|---|
| EPSG code | EPSG:4326 | EPSG:3857 |
| Name | WGS 84 | WGS 84 / Pseudo-Mercator (Web Mercator) |
| Type | Geographic | Projected |
| Units | degrees | metres |
| Datum | WGS 84 | WGS 84 |
| Area of use | Worldwide | Worldwide (web mapping), roughly 85°S to 85°N |
| proj4 | +proj=longlat +datum=WGS84 +no_defs | +proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +no_defs |
When to use EPSG:4326
Use EPSG:4326 for storing, exchanging and analyzing data: GeoJSON output, APIs, databases, GPS, and anything where a degree value should mean a real position on Earth. It is the safe default for portability.
When to use EPSG:3857
Use EPSG:3857 when feeding a web map's tile/rendering layer that expects projected meters, or matching a basemap that is already in Web Mercator. Avoid it for measuring real distances or areas, especially at high latitudes, where its distortion is severe.
Converting between EPSG:4326 and EPSG:3857 is a reprojection, not a relabel. Convert and reproject a file or detect your CRS.
Frequently asked questions
What is the difference between EPSG:4326 and EPSG:3857?
EPSG:4326 (WGS 84) expresses positions as longitude/latitude in degrees; EPSG:3857 (Web Mercator) projects them to meters on a flat plane for web map tiles. Same datum, different units and number ranges, and 3857 distorts area toward the poles.
Is GeoJSON in 4326 or 3857?
GeoJSON (RFC 7946) is defined in WGS 84 (EPSG:4326) — longitude/latitude in degrees. If you have GeoJSON with meter-scale coordinates, it is non-standard 3857 data and most tools will misplace it.
Can I just relabel 4326 data as 3857?
No. The numbers genuinely differ — degrees versus meters — so converting requires reprojection (a Mercator forward or inverse transform), not just changing the CRS label.
Why does Greenland look huge on a web map?
That's Web Mercator (3857). It preserves angles for seamless tiling but inflates area increasingly toward the poles, so high-latitude landmasses like Greenland appear far larger than they are.