When dataviz makes the front page!

Not sure if you saw it, but last Friday a data visualization debate was all over the news:

The issue being debated is one of the most common dataviz caveats. (Note that I have a collection of such caveats here!)

It's a well known one, but I could not miss the opportunity! So here is briefly what happened, what the caveat is, and why it's not that simple.

What actually happened

On September 4, the UN General Assembly adopted a resolution encouraging countries to move away from the Mercator projection, and to use the Equal Earth projection instead.

The text was pushed by Togo and backed by the African Union. It passed with 164 votes in favour.

Nothing is banned. The resolution only encourages governments, schools, media and tech companies to use equal-area projections when the relative size of countries matters.

So it is just a recommendation about a default. But defaults are powerful! We are surrounded by world maps. The way we draw our planet definitely has an impact on how we picture it in our heads.

Mercator: a great map, used for the wrong job

Gerardus Mercator published his projection in 1569, with one very specific goal: helping sailors.

On his map, a straight line is a constant compass bearing. You draw a line from Lisbon to Recife, you follow the angle, you arrive. In the 16th century, that was a revolution.

But you cannot flatten a sphere for free. Something always has to break. Mercator chose to preserve angles and shapes, and he paid for it with area.

The further you get from the equator, the more the map inflates things. And it inflates a lot. On Mercator, Greenland looks about the same size as Africa. In reality, Africa is 14 times bigger.

This gif comes from thetruesize.com. It lets you drag a country around and watch its real size appear. It explains the problem better than any paragraph I could write.

Equal Earth: the other trade-off

Equal Earth is another projection, surprisingly recent.

It is an equal-area projection: the same amount of pixels always represents the same amount of square kilometers. Africa is 14 times Greenland on the map, because Africa is 14 times Greenland in real life.

But there is a price to pay. Going straight north or south no longer means following a straight line on the map. And continents end up squashed, vertically pulled. That is the trade-off.

Of course, I could not resist building a little playground with React and D3.js to show the animation between both options:

By the way, if you are wondering how to build such a smooth transition, it is surprisingly approachable now with AI helping along the way. I teach exactly this here.

The bottom line

No projection is perfect. Equal Earth preserves area but distorts shapes and angles. Mercator does the opposite. Every flat map lies about something.

Anyway, it makes me happy that millions of people who never think about dataviz were arguing about a projection choice. Data visualization keeps reaching a wider audience, and that is very good news.

See you next week!
Yan