Welcome to the New World Map

Yesterday the UN General Assembly voted to replace its traditional world maps - based on Mercator - with a map that more accurately reflects the size of Africa - based on the 2018 Equal Earth map.

My Equal Earth vs Web Mercator map allows you to compare how these two maps depict the world side-by-side. Drag the handle in the middle of the map and you can switch between the two projections. You can also pan and zoom around the map and the two views will move together.

Equal Earth vs Mercator

The problem with Mercator isn't that it is a "bad" map. Quite the opposite: Gerardus Mercator's 1569 projection was designed for sea navigation, where preserving angles and directions is enormously useful. The problem is that it is a rather unfortunate choice when you want to compare the size of countries and continents.

Mercator increasingly exaggerates areas as you move away from the Equator. Greenland is the classic example. On a conventional Mercator world map it can look comparable in size to Africa, whereas Africa is actually about 14 times larger.

Equal Earth was designed to solve precisely this problem. Developed by Bojan Šavrič, Tom Patterson and Bernhard Jenny and published in 2018, it is an equal-area projection. Countries and continents therefore retain their correct relative areas, although their shapes are inevitably changed in the process.

And that's the important distinction here: Equal Earth doesn't make everything "accurate". It makes area accurate. There is no flat world map that can preserve everything about the spherical Earth at once. Every projection involves compromises between properties such as area, shape, distance and direction.

Making Equal Earth vs Web Mercator Map

For the Equal Earth side of the map I used the rather ingenious web-mapping work of bbox.earth, which provides Natural Earth vector tiles projected using Equal Earth but arranged on a Web Mercator-style tile grid.

This is particularly useful because MapLibre (the map library used for my map comparison tool) is built around Web Mercator. Rather than trying to persuade MapLibre to suddenly become a completely different projection, the Equal Earth data is prepared so that it can be displayed using MapLibre's normal tile machinery. The bbox.earth example is remarkably simple: the map is essentially just a MapLibre map pointing at their Equal Earth Natural Earth style.

For the other half I used the OpenFreeMap Liberty style, which is a conventional Web Mercator web map.

I then put the two maps on top of one another and added a draggable vertical divider. The Equal Earth map is clipped at the position of the divider, revealing the normal Web Mercator map underneath. The two maps are also synchronised, so moving one moves the other.

There is one additional wrinkle. The bbox.earth Equal Earth tiles use a slightly smaller world extent than the corresponding Web Mercator grid and are displayed with a 1.162 scale factor. I compensate for that by applying the equivalent adjustment to the MapLibre zoom level when synchronising the two maps.

A Word of Caution

There is an important caveat to this experiment.

Don't treat the swipe as a precise, pixel-for-pixel comparison of the two projections.

The two maps are using different projections, so geographic features cannot simply be expected to occupy the same screen positions. We are synchronising their geographic centre and making a scale adjustment, but the mathematical transformation of latitude and longitude is fundamentally different in the two maps.

There's also a more fundamental difference between the two map layers. The Equal Earth side is using Natural Earth data supplied through bbox.earth, while the Mercator side is using OpenFreeMap. So although both maps depict the same world, they aren't literally using the same underlying vector data and styling.

In other words, this is a visual demonstration rather than a rigorous cartographic comparison.

And that's probably fine. Dragging the divider across Greenland or Africa makes the central point rather effectively: the shapes and positions of countries change between projections, but the most striking change is how their relative areas are represented.