Map projections explained
Every flat map of the round Earth distorts something. Switch projections and watch the red circles: they are all the same size on the globe, so anything that changes about them is distortion.
Mercator
- Created
- 1569, Gerardus Mercator
- Preserves
- Angles and local shapes (conformal). Straight lines are constant compass bearings.
- Distorts
- Area, badly: sizes balloon toward the poles and the poles themselves can never be shown.
- Used for
- Sea navigation; web maps (Google, Apple, OpenStreetMap use Web Mercator).
Why you can't flatten a globe
Try pressing an orange peel flat: it tears or stretches. A sphere has what mathematicians call positive curvature, and Gauss proved no flat map can keep all distances, areas and angles at once. So mapmakers choose. Conformal projections like Mercator keep angles, so the Tissot circles stay round, but their size changes. Equal-area projections like Equal Earth and Gall–Peters keep every circle's area, so they squash into ellipses instead. Compromise projections like Winkel Tripel let everything be a little wrong so nothing is very wrong.
See Mercator's size distortion up close by dragging countries on the true size map, or find out why the shortest flight path looks curved on the distance calculator.
Globes and flat maps both begin with the same sphere lit by the Sun; if you want to see that light play across the Moon instead, ahaboo lets you orbit it around Earth and watch the phases change.
Frequently asked questions
What is the most accurate map projection?
None is accurate in every way. The mathematician Carl Friedrich Gauss proved in 1827 (his Theorema Egregium) that a sphere cannot be flattened without distortion. You choose what to keep: area (Equal Earth, Gall–Peters), angles (Mercator), distance from one point (azimuthal equidistant), or a balance (Winkel Tripel, Robinson).
What projection does Google Maps use?
Web Mercator, a simplified Mercator. It keeps streets and buildings at the right shape at any zoom, which matters more for directions than showing continents at their true size. Zoomed out, Google Maps switches to a 3D globe.
What is Tissot's indicatrix?
A set of identical small circles drawn on the globe and then projected. How they change shows distortion: on Mercator they stay round (shape is kept) but grow toward the poles (area is not); on equal-area maps they keep their area but squash into ellipses.
Why is Mercator so common in schools?
Historical habit: it was the standard for navigation charts for centuries and printed wall maps copied it. Many educators now prefer equal-area projections for world maps so pupils don't learn a distorted picture of relative size.