Map Projection Reference
Searchable reference for common map projections — what each is good for.
Overview
The Map Projection Reference is a searchable cheat-sheet for the most common map projections you will encounter in GIS, cartography and web mapping. Each entry summarises what the projection looks like, what it preserves (shape, area, distance or direction), and what it is good for. Filter by name, by property, or by typical use case to find the right projection for your map.
There is no single best projection - every flattening of a sphere onto a plane distorts something. The reference here covers the projections you actually meet in the wild: Mercator and Web Mercator for online maps, Equal Earth and Robinson for world thematic maps, UTM and State Plane for surveying, Lambert Conformal Conic for aeronautical charts, and a handful of specialist projections such as Azimuthal Equidistant for radio range planning.
How it works
Map projections are mathematical functions that map points on the WGS84 ellipsoid (or its spherical approximation) to a 2D plane. Each projection optimises for one or more properties at the cost of the others: conformal projections preserve angles (so shapes are locally correct), equal-area projections preserve area (so country sizes look right), equidistant projections preserve distance along certain lines, and azimuthal projections preserve direction from a chosen centre.
The reference groups projections by these properties and tags each one with its typical EPSG code where applicable - for example Web Mercator is EPSG:3857, WGS84 geographic is EPSG:4326, and British National Grid is EPSG:27700. The EPSG identifier is the lingua franca of GIS software, so having it handy speeds up configuration.
Examples
- Web Mercator (EPSG:3857) - conformal, badly distorts area near the poles, but the standard for slippy map tiles because the equations are simple and squares stay square.
- Equal Earth - pseudocylindrical equal-area, designed in 2018 as a friendlier alternative to Robinson and Winkel Tripel for world thematic maps.
- UTM zones (EPSG:326xx for north, 327xx for south) - transverse Mercator strips 6 degrees wide each, conformal, used for surveying and military maps.
- Lambert Conformal Conic - conformal, the standard for aeronautical charts and many national grids in mid-latitude countries.
FAQ
Is Mercator the same as Web Mercator?
Almost. Web Mercator (EPSG:3857) uses the WGS84 ellipsoid coordinates but applies Mercator's spherical formula, which produces a small but non-zero discrepancy with the strictly correct ellipsoidal Mercator (EPSG:3395). For most web mapping this difference is irrelevant.
Which projection should I use for a thematic world map?
For area-based statistics (population, GDP), pick an equal-area projection such as Equal Earth, Eckert IV or Mollweide. Mercator badly oversizes high-latitude countries and is a poor choice for any choropleth.
What is an EPSG code?
A registry-issued integer that uniquely identifies a coordinate reference system. GIS tools use EPSG codes to look up the projection's equations and parameters.
Why not always use lat/lng?
Geographic coordinates work for storage and many calculations, but they are not a map projection - drawing them directly on a screen gives plate carrée, which distorts both shape and area. Picking the right projection matters whenever the map will be looked at.