WGS84 / Pseudo-Mercator (EPSG:3857)
Apr 14,2026

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Introduction

WGS84 / Pseudo-Mercator (EPSG:3857) is a projected coordinate system widely used in modern web mapping services. It is based on the WGS 84 geographic coordinate system and employs a simplified version of the traditional Mercator projection adapted for web display. Primarily designed for rendering tile-based web maps, it serves as the standard display coordinate system for online map services and GIS platforms. By converting geographic coordinates expressed in degrees to plane coordinates in meters, it facilitates fast map rendering and zooming operations.

Coordinate System Composition

WGS84 / Pseudo-Mercator (EPSG:3857) is not a format with a file structure but is defined as a map projection and coordinate reference system. The main components are as follows:

Geodetic CRS: The underlying geographic coordinate system is WGS84, which defines geographic positions using an Earth ellipsoid model.
Projection Method: A pseudo-Mercator projection based on the Mercator projection is used, projecting the Earth's surface onto a cylinder and then developing it onto a plane.
Coordinate Unit: Geographic coordinates (degrees) are converted to plane coordinates (meters). This improves the efficiency of distance calculations and tile rendering.
Extent: The X coordinate ranges approximately from ±20,037,508.34 meters, with the Y coordinate defined over a similar range, enabling the entire world map to be represented.
Tile-based Rendering: In web maps, this coordinate system is used in combination with a tile structure divided by zoom level to achieve fast map display.

Pros

High compatibility with web maps: EPSG:3857 is adopted as the standard in many web map services and has very high compatibility with tile-based map display.
Fast rendering performance: Because coordinates are converted to a meter-based plane coordinate system, map display operations such as zooming and panning can be performed efficiently.
Broad software support: The system is natively supported by most GIS software and web mapping libraries.
Good affinity with tile maps: It works well with the tile approach of dividing maps by zoom level, maintaining high performance even for large-scale map services.

Cons

Large area distortion: In high-latitude regions, areas are greatly exaggerated and appear significantly different from their actual geographic areas.
Limited polar representation: Although the projection theoretically extends to the poles, actual web maps typically display only up to approximately ±85.051° latitude.
Unsuitable for geodetic accuracy: It is not suitable for precise distance or area measurements, and for analytical purposes, other projected coordinate systems must be used.
Does not fully reflect the ellipsoid: Because it is a simplified pseudo-version of the Mercator projection, it is not suitable for rigorous geodetic calculations.

Application Scenario

WGS84 / Pseudo-Mercator (EPSG:3857) is primarily used in web maps and online geographic information services. Typical applications include online map display, geographic information platforms, navigation apps, and urban information systems. In particular, it is adopted as the standard coordinate system for tile-based map services, enabling high-speed delivery and display of large-scale map data. It is also widely used in GIS applications as a display coordinate system to ensure compatibility with web maps.