What is the Mercator projection?
Gerardus Mercator published it in 1569 as a chart for sailors. Its one job was to make a straight line on the map equal a constant compass bearing at sea. To do that, Mercator spaced the lines of latitude further and further apart towards the poles, exactly as much as the lines of longitude spread apart on the real globe. Every small shape stays true, every angle stays true, and area pays the price.
The stretch at any latitude is 1 divided by the cosine of that latitude, applied in both directions. So area is multiplied by 1 / cos². The poles themselves can never be drawn, because the factor becomes infinite, which is why Mercator maps stop at around 85°.
How much does Mercator distort each latitude?
| Latitude | Area shown | Places at this latitude |
|---|---|---|
| 0° | 1.0× | Kenya, Ecuador, Indonesia |
| 30° | 1.3× | Egypt, Florida, Shanghai |
| 45° | 2.0× | France, Mongolia, Minneapolis |
| 60° | 4.0× | Oslo, Helsinki, Anchorage |
| 72° | 10.5× | Middle of Greenland |
| 80° | 33.2× | Northern Greenland, Svalbard |
Read the table against a globe. Most of Europe sits between 40° and 60° north, so it is drawn at two to four times its true area. Canada and Russia straddle 60°. Africa, South America and Southeast Asia sit within 35° of the equator and are drawn close to true size. That is why the northern countries look large and the tropical ones look small: the map is stretching one and leaving the other alone.
Which countries look most wrong?
- Greenland is drawn at about 10 times its area. It looks as big as Africa; Africa is 14 times bigger. True size of Greenland.
- Russia (17,098,246 km²) looks bigger than Africa (30,030,427 km²). Africa is 1.8 times bigger.
- Canada (9,984,670 km²) looks close to Africa in size. Africa is 3.0 times bigger. True size of Canada.
- Antarctica is drawn as a band along the bottom of the map that is wider than every other continent combined. It is 14.2 million km², smaller than Russia and Canada together.
- Scandinavia: Norway, Sweden and Finland are drawn at four to five times their area. Sweden (450,295 km²) looks as big as Egypt (1,002,450 km²) and is less than half its size.
- Brazil, DR Congo and Indonesia are the opposite case. They sit on the equator, are drawn at close to true size, and look small next to their inflated northern neighbours. Brazil (8,515,767 km²) is bigger than the whole of Europe without Russia.
Why does Google Maps use it, then?
Because Google Maps is a navigation tool, and Mercator is the best projection there is for navigation at street level. North is up everywhere. Streets that meet at right angles on the ground meet at right angles on the screen. The whole world divides cleanly into square tiles that double in detail at each zoom level, which is what makes smooth zooming from a continent to a doorway possible. Google adopted Web Mercator in 2005 and every major web map followed.
None of that helps you compare Brazil with Greenland, but comparing countries is not what the product is for. On the desktop site Google now shows a globe when you zoom all the way out, a change made in August 2018. The phone app and every zoomed-in view remain Mercator.
See the same world in Perspective Map
Perspective Map does not use a projection at all. Each of its 185 countries is a box, and the area of the box is exactly proportional to the number you choose: total area, population, density, GDP per person or total GDP. Nothing is stretched, so any two boxes can be compared by eye.
Take the Russia and Africa example. On Google Maps Russia looks like the bigger of the two. Drop Russia into Africa in Perspective Map and it becomes the largest box on the continent, 7.2 times Algeria, yet the 54 African boxes together are still 1.8 times larger than Russia's. Then switch the perspective to population: Russia's box shrinks to 144 million people and Nigeria's grows to 238 million, and the picture changes again. That switch, from one measure to another with the same countries in the same places, is what a map cannot do.
What should you use to compare country sizes?
An equal-area projection, or no projection at all.
- Equal Earth (2018, by Bojan Šavrič, Tom Patterson and Bernhard Jenny) keeps area exact and shapes close to familiar. Perspective Map's Atlas view uses it.
- Gall-Peters (1855, popularised in the 1970s) keeps area exact but stretches shapes badly near the equator.
- Winkel Tripel does not keep area exact but spreads the error evenly. National Geographic has used it for its world maps since 1998.
- Boxes, as above: area matches the figure exactly, and the same box can show population or GDP.
Questions people ask
Is Google Maps wrong?
Not for what most people use it for. Directions, street layouts and distances inside a city are accurate, because Web Mercator keeps shapes and angles correct over small areas. It is wrong for comparing the size of countries, and the error grows the further you are from the equator.
Why does Google Maps use the Mercator projection?
Because it keeps north pointing up everywhere, keeps street corners square, and lets the whole world be cut into square tiles at every zoom level. Those properties matter for navigation. Equal-area maps give them up.
Does Google Earth have the same problem?
No. Google Earth shows a globe, and a globe has no projection distortion. Google Maps on desktop also switches to a globe when you zoom all the way out, a change made in 2018. The mobile app and every zoomed-in view still use Web Mercator.
What is the most accurate world map?
No flat map can keep area, shape, distance and direction all correct at once; that is a mathematical fact, not a design failure. For comparing size, use an equal-area projection such as Equal Earth (2018), Mollweide or Gall-Peters. For navigation, Mercator. For a balanced general-purpose wall map, Winkel Tripel, which National Geographic has used since 1998.
How much bigger does Mercator make Greenland?
About 10 times by area at its central latitude of 72° north. Greenland is 2,166,086 km²; Africa is 14 times larger, but Mercator draws them at about the same size.
Which projection does Perspective Map use?
None for the main view: every country is a box whose area is exactly proportional to the data, so there is nothing to distort. The Atlas view places those boxes on an Equal Earth map, and the Google map tab shows the same countries on Web Mercator so you can see the difference.