The Mercator projection
Mercator is the map on most phones and websites. It's brilliant at one job — keeping compass directions straight — and it does that job so well that it ended up everywhere, even in places where that job doesn't matter.
Key facts
- Family
- Cylindrical, conformal
- Designer
- Gerardus Mercator
- Year
- 1569
- Preserves
- True shape and True direction
- Best for
- Marine and air navigation, and street-level web maps (Web Mercator)
- Weak at
- Area — land far from the equator is stretched enormous
What it looks like
On a Mercator map, every line of longitude runs straight up and down, parallel to its neighbors, like a grid drawn on graph paper. That's different from the globe, where those lines actually squeeze together toward the poles. Mercator stretches them back apart to keep the grid straight, and stretches everything else along with them.
What it keeps true
Compass directions. If you draw a straight line on a Mercator map and follow that exact compass heading the whole way, you'll actually get where the line points. That sounds obvious, but it's not true on most other maps.
What it distorts, and why
Size, especially near the North and South Poles. To keep those compass lines straight, Mercator has to stretch land more and more the farther it is from the equator. That's why Greenland looks like it's competing with entire continents on a Mercator map, even though it really isn't close.
A short history
Gerardus Mercator published this map in 1569 to solve one specific problem: helping ship captains sail a straight compass course without constantly redoing their math. For sailors crossing open ocean with no landmarks, that was a huge deal.
Where you meet it today
It's still the map on your phone. That's mostly a coincidence of how web maps are built: they're made of tiny square tiles that have to line up perfectly at every zoom level, and Mercator's straight grid makes that easy. It's genuinely the right map for a phone navigating city streets — it just isn't the right map for comparing how big countries are.
Try it yourself
Frequently asked questions
Why does Greenland look so big on the Mercator map?
Mercator has to stretch land more and more the farther it is from the equator in order to keep compass directions straight everywhere. Greenland sits at a high latitude, so it gets stretched a great deal, making it look like it rivals whole continents even though it really doesn't come close. Switch to an equal-area projection like Equal Earth and Greenland shrinks back down to its true proportions.
Is the Mercator projection wrong?
No — it's right for the job it was built for. Mercator keeps compass directions and shapes true everywhere, which is exactly what sailors needed to plot a straight course, and it's genuinely useful today for navigation and zoomable street maps. It's only a problem when it's used for a job it was never designed for, like comparing how big countries are.
What projection do web maps like Google Maps use?
Almost all of them, including Google Maps, use a version called Web Mercator. It's popular mainly because its straight grid tiles cleanly into square images at every zoom level, which made it easy to build fast, scrollable maps in the early web-mapping era, not because it's the best map for judging country size.
Why is Mercator still used if it distorts size so much?
Because size distortion isn't the point of most of its modern uses. Street-level navigation apps care about direction and local shape, both of which Mercator preserves perfectly, and its straight grid happens to make map tiles easy to build. The size distortion only becomes a problem when someone uses it to compare whole countries or continents, a job it was never meant for.
What is a rhumb line?
A rhumb line is a path that holds one constant compass bearing the entire way, like always steering exactly northeast. On a globe, a rhumb line curves. On a Mercator map, it's always a straight line, which is exactly why sailors could plot a course with a ruler and then just hold that one heading the whole voyage.