Projection distortion

A quick fix to a map today, courtesy of Ed Hawkins over at better figures-approved blog Climate Lab Book.

Ed asked “When will we reach 2°C?“, and posted this great map, showing areas of the world that have risen already by 2°C* in the last century or so.

BlVb09eIAAAroLe.png:large

There is a nice use of appropriate colour palettes here, in my opinion. Red and blue make sense for warming and cooling, and the threshold is clearly marked in the shift to purple, perhaps in a cheeky reference to the “Australia so hot it needs new colours” story. Also, we can’t see any green, can you?

However, we’ve known for ages that using any map projection distorts areas and distances, and that in turn can distort your interpretation of the data presented in the map. Ed’s map looks like it distorts in a similar way to the Mercator projection, which is great for some things, but which exaggerates the area of the poles a great deal. And if those are the areas where your interesting data are, then, well, you can see what might happen.

When potential skew was pointed out, Ed (being a helpful sort of fellow) immediately created a new map. This one looks closer to a Mollweide projection to me.

BlWHNwBCAAAa02a.png:large

No map projection is perfect, but some are better than others – depending, of course, on what you are trying to communicate.

As usual, it is probably best to let XKCD have the last word.

 

Notes

*For context a global change of two degrees is considered by the UN to be “dangerous”, although arguments of that sort aren’t really the point here at BF.

 

 

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One comment

  1. […] (16/04/14): The Better Figures blog discusses the map projection used in the figures below. An alternative Mollweide projection version is […]

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