The Mercator projection, explained

The Mercator projection is the famous "old world map" — a formula published by Flemish cartographer Gerardus Mercator in 1569 for sea navigation. It does one thing brilliantly: any compass bearing drawn as a straight line on the map is a straight course a ship can follow.

How distortion grows

To keep all those lines straight, Mercator stretches distances more and more with latitude. At 60° north the map is stretched roughly 4×; near the poles it is effectively infinite. The land itself does not need to stretch everywhere — the stretching is uniform in all directions at a given latitude, so shapes stay mostly recognizable, but areas balloon. That is why Greenland (actually ~13th largest territory on Earth) is drawn larger than Africa, and why Canada and Russia look like giants.

Where Mercator is still the right tool

Marine charts, GPS navigation displays and any map whose job is finding the bearing between two points still use Mercator or its close cousins. "Wrong" is the wrong word — it is the wrong map for comparing sizes, but the right map for compass navigation. See the difference yourself on the old map vs new map page.

Equal Earth Projection — the True-Size World Map, Explained Mercator vs Equal Earth — Which World Map Is Better?Old vs New World Map

Facts & figures

Why was the Mercator map invented?

For navigation. Before 1569, sailors could not easily chart a constant compass course on paper: Mercator's projection makes any straight line on the map a line of constant true bearing (a rhumb line). It solved a deadly real-world problem — at the price of inflating high-latitude land.

Is the Mercator map wrong?

Not for its job. Mercator is a distortion, not an error — every flat map distorts something. It distorts area badly, so it misleads anyone comparing country sizes: Africa is about 14 times larger than Greenland, not smaller. For that question, an equal-area map like Equal Earth is correct.

How much does Mercator distort area?

Inflation equals 1/cos(latitude)². At 30° it is ~1.3×, at 45° ~2×, at 60° ~4×, at 70° ~8.5× and at 80° ~33×. This is why equatorial countries look real and northern ones blow up.