Geographers must know about… Map Projections

I have a lot of arguments, or at least gentle disagreements with colleagues, about whether there is a core of fundamental geographical knowledge that any self-respecting Geographer needs to know about. I say of course there is. Yes, Geography is a broad and eclectic church, but if you aren’t anchored to the core of the discipline and all you have are your esoteric specialisms, then eventually you lose touch with the mothership and pooph! you aren’t a Geographer any more. So long. Look at a map and come back soon.

Looking at a map, of course, is an appropriate reference in this case, because if there is any one thing sitting at the common core of all geography it is the map-ness of the discipline. If you have something that you can’t put somehow on some sort of a map, then you’ve found something that isn’t Geography.

So one of the first things a Geography student needs to be aware of is that maps are not as simple as you might have imagined before you became a geographer. Geography students need to know about “map projections”. Take the straightforward World Map, for example. The world is in reality a sort of roundish globular shape in three dimensions (if you are already a Geographer you are probably congratulating yourself now for knowing the word ‘geoid’). A world map is typically a two-dimensional sheet of paper or some fancy electronic equivalent. Now, if you go and buy yourself a roundish globular cardboard or blow-up globe, and try to flatten it out into a flat sheet on your table top you will quickly find that you can’t spread a globe out into a sheet without stretching bits or cutting it up in wild slices. As you stretch and twist and cut and try to make the best approximation that you can, what you are doing is trying out different map projections. People have been doing it for centuries. Every map you look at is someone’s choice of the best way to twist and stretch and slice the globe to make it flattish.

The world map that most people are familiar with is a projection devised by a man called Mercator in the 1560s. The Mercator projection is brilliant for navigation because it is stretched and twisted in just such a way that directions on the map are exactly the same as compass directions on the real earth. However, the Mercator projection is also rubbish, because in order to make the directions and navigation work right it had to squeeze up all the distances at the equator and stretch them more and more as you move towards the poles. The result is that all the sizes and shapes of everything on the map are completely wrong. You might wonder why the map ever caught on, but it did, and one result of its popularity is that most people have a completely false idea of how big or small different places are. Most people massively wrong about the sizes of Africa, Australia, North America, South America, well… everywhere. On the standard Mercator World Map, Greenland looks huge and Australia looks quite small, although in reality Australia is three times bigger than Greenland. Mercator shrinks Africa and Brazil, for example, but expands North America and Europe.

You may now be thinking that you’ll throw away Mercator and use a better projection, but when you look into it (as you should) you will find that there is no map projection that overcomes the problem of squeezing and stretching a globe onto a sheet. It is a fundamental problem for cartography, and the choices that we make when we decide which map projection to use for any job have a fundamental impact on what our mapped data will look like. Choosing a different map projection, perhaps because we need the areas of places to be correct, or because we need the shapes to be right, or because we need directions on the map to match directions on the compass, will give us a quite different version of reality. And whichever projection you choose (there are lots to choose from) there will always be something about it that is inaccurate. You can’t have a two-dimensional map of our three-dimensional globe without accepting compromises that introduce inaccuracies.

Maps are wrong. You are a Geographer, so you need to face up to this.

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PS – here’s a useful web page that lets you compare how wrong different projections are! https://s3.amazonaws.com/thetruesize.com/mockup.html#aboutModal

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