Chances are, most of the maps you look at use a Mercator projection. Or, to be more accurate, a slightly modified version called a Web Mercator projection. That’s because every time you use your phone or computer to get directions, Google, or Bing, or Mapquest (gasp!) shows you this projection. That would be ok, because Mercator is a conformal projection, which means it preserves local angular relationships, making it great for viewing roads in your city. But Web Mercator isn’t even conformal, so really it’s not ideal for anything! Oh well…as long as you get to your destination, I suppose it doesn’t really matter.

The purpose of this graphic is to illustrate that, while Mercator has become the default perception of the world for many, it creates a severely distorted view because it grossly exaggerates areas near the poles, as can be seen using Tissot’s indicatrix. If you aren’t familiar with this tool, read this article. So while Mercator is great for local viewing, it’s painful to look at on a global scale.

When selecting a projection, it’s important to consider how the map is going to be used. Are you going to be measuring distances? Angles? Areas? If so, choose a projection that preserves the quality of interest. For comparing the area of Greenland to Africa, we need to use equal-area projections like sinusoidal or Mollweide. If you use Mercator, you’ll make the mistake of thinking that Africa is slightly smaller than Greenland; the Africa to Greenland area ratio is 0.9 in a Mercator projection, as opposed to its true ratio of 13.9. If you are making a global thematic map that just needs to look pretty, find a projection that suits you. Just make sure it isn’t Mercator.

Data source: http://resources.arcgis.com/en/help/main/10.1/index.html#/List_of_supported_map_projections/003r00000017000000/

Inspiration:

https://xkcd.com/977/

http://www.pratham.name/mercator-projection-africa-vs-greenland.html (Note that many other sites have compared the areas of Greenland to Africa using varying projections – this is just one example.)