How the Mercator Projection Won the Internet

Published on by Jonathan Crowe
OpenStreetMap, using Web Mercator, all zoomed out
OpenStreetMap

I’ve said it before: if you want to start a fight among cartographers, ask them what their favourite map projection is. Earlier this week I did just that: I felt mischievous and wanted to try out Twitter’s polling feature, so I ran a poll asking my Map Room followers what the best projection for world maps was. And because I was feeling particularly mischievous, I made sure to include both the often-reviled Mercator projection and its antithesis, the Peters projection, rounding out the list with two less controversial choices: the Winkel tripel projection used by National Geographic, and the brand-new Patterson projection announced late last year.

The results of the poll were utterly unexpected: 42 percent chose the Mercator projection.

I was trolling the Internet, pure and simple, and in the end I got trolled back. Fair enough.

Then again, maybe I wasn’t. The more I thought about it, the more I realized that, whether they knew it or not, the voters had a point. Because when you think about it, the Mercator projection has won in the cartographic arena that really matters today: online mapping.

Every online map service uses a variant of the Mercator projection called Web Mercator. Whatever its shortcomings—and there are many, owing to the fact that its calculations use a spherical Mercator model to save computational cycles—Web Mercator has become the de facto standard. And the size distortions at small scales that have made the Mercator projection the target of so much ire over the decades are simply moot for most use cases.

In many ways the past debates over the Mercator are moot: arguing over the right projection for wall-sized world maps—Mercator vs. Peters vs. Robinson—is fighting the last war. Mercator has become the default option for online mapmaking, simply because so many data visualization maps rely on Google Maps or OpenStreetMap for their base map layer. Other projections will be reserved for the professionals, people with access to more sophisticated mapmaking tools and the skill to use them, but for the most part, when data is mapped on the Internet, it’ll be mapped according to Mercator.

(For more on the controversy surrounding the Mercator projection, read Mark Monmonier’s Rhumb Lines and Map Wars: A Social History of the Mercator Projection. I reviewed the book in 2008.)