Thursday, 31 January 2013

Which world map projection is correct?

A recent Google map puzzle got me thinking once again about map projections and the ways in which they can be used for web maps. Google maps uses a variation on the Mercator projection which, as we all know, dates from 1569. Most people who are into maps know that this particular projection makes areas close to the poles look bigger than they actually are. This distortion is an unavoidable problem when trying to project the surface of a big round object like the earth on to a flat surface. So, which world map project is correct? The answer is of course that none are 'correct' or possibly that there can be no 'correct'. Every projection compromises something. To demonstrate this I've mapped the world nine different times in the image below to demonstrate the impact of using different projections.

I've pasted the individual images below and you should be able to flick through them for comparison by clicking on one and then clicking to see each successive image. Two that I think are particularly effective are the Robinson and the Winkel Tripel. These have both been used by National Geographic. The former was their default projection until 1998 when they switched to Winkel Tripel, which was originally developed by Oscar Winkel in 1921. Equal area projections are of course used widely (e.g. Gall-Peters) but some suffer from extreme flattening at the poles, like the Behrmann one below. No matter what, none are really 'correct'.

Now I should get back to marking reports!