Map projections

When you look at different world maps, you’ll notice that they don’t look exactly alike. Compare this map here with, for example, this one. Here, the continents are thin and tall. It’s as if they have been stretched up and down except for the very north and the very south. There, it’s as if this map has been flattened.

How come these maps don’t look alike? Well, when you take a sphere and try to show the round surface on a flat piece of paper, it’s not possible to make a perfect representation. Let’s cut this beach ball open, and try to transform it into a flat surface. We have to pull and stretch it, and when we do, the circles on the beach ball change. If we do the same with the surface of the earth, cut it open and stretch it into a flat surface, a map, the continents change in shape and size.

The map has distortions. So the continents on our map don’t look exactly like those on a globe, but why do flat maps vary? Because we can stretch the surface of the earth in various ways. We say that we make different projections of the world map. A flat map distorts the shapes, sizes and distances between the continents, in some way.

All projections have distortions. But which map is best? Here, the continents have about the same shape as on the globe. South America, Australia. The map conserves shape.

But look! The distances between Mogadishu and Kuala Lumpur, and between Reykjavik and Saint Petersburg look equal. The lines are about the same length. Now look at the globe! It is in fact twice as far between Mogadishu and Kuala Lumpur.

So, this map is not very good if we want to compare distances, and therefore it’s also not very good at describing sizes. If we drag Greenland down to Africa, they seem to have about the same size. On the globe we see that this is not true. Africa is a lot bigger than Greenland. This kind of projection was first made as early as the 16th Century by Gerardus Mercator.

We call it Mercator’s projection. It conserves the continents’ shapes, but it distorts sizes and distances. Is it possible to do it some other way? So that size and distance are more correctly represented? Let’s look at our other map, and compare Greenland on this map with Greenland on the globe.

The size seems about right, but the shape of the island is heavily distorted. Africa on this map is also about the same size as on the globe. But the shape of Africa is also stretched, distorted. This is Gall-Peters’ projection. This map looks a bit strange, but all oceans and continents are there.

This is Africa, Australia, and South America. Both size and shape of the continents are shown fairly accurately. But look at the oceans! It’s like they are cut apart. This projection is interrupted.

Let’s mark some cities, London and New York, and draw a line between them. Here’s Cape Town and Sao Paolo, and a line between them. Which distance is the shortest? It’s not easy to tell, as the lines go through the white areas, off the map. This is Boggs’ projection.

It displays shape and size in a rather good way, but it is more difficult to assess and compare distances. And then there are two shapes on the map which match the globe very badly. Can you see them? They are Greenland and Antarctica, which are cut into parts. None of these maps is “the best”.

Different maps are useful for different purposes. Which projection is best suited depends on what you want to do with the map, for instance compare the size of countries, or see their shapes. The most common projection you’ll meet is probably this one: Mercator’s projection. Gall-Peters’ projection, though, is unusual. Perhaps it’s because most maps are drawn and printed by Europeans and North Americans, in the richer parts of the World.

They use Mercator’s and similar projections, and don’t mind that Europe and North America look larger than they actually are. Or maybe it’s because none of the continents on the Gall-Peters’ projection have the right shape, compared with the globe. The map, simply, is not very good. These are three well known map projections. There are many more.

And all projections in some way distort the shapes, sizes or distances between the continents.