3857

3857 refers to the EPSG code 3857, officially named WGS 84 / Pseudo-Mercator. It is a widely used coordinate reference system in web mapping, the de facto standard for online map tiles and many geographic information systems.

The projection is a variant of the Mercator projection that treats the Earth as a sphere with a radius of 6378137 meters. In this system, x coordinates correspond to longitude scaled linearly, while y coordinates are derived from latitude using the mercator transformation. The result is a planar, meters-based grid that renders well on square map tiles and supports constant loading across a map canvas. The projection is conformal, preserving local angles, but it is not equal-area and distorts distance and area increasingly toward the poles.

Usage and impact: EPSG:3857 underpins major web mapping platforms such as Google Maps, Bing Maps, OpenStreetMap, and many GIS tools. ItUnderpins the common Web Mercator tiling scheme, enabling efficient tile generation, caching, and seamless panning and zooming across the globe.

Limitations: Because it uses a spherical model, it is only an approximation of true geographic coordinates on the WGS 84 ellipsoid. Distortions rise with latitude, making measurements less reliable for precise distance or area calculations. The projection is typically capped at about 85.0511 degrees latitude to avoid infinite values at the poles.

Notes: It is sometimes called Web Mercator or WGS 84 / Pseudo-Mercator and should not be confused with the true Mercator used in nautical contexts.