Why we (still) use the Mercator projection 🗺️ - a-thousand-channels/ORTE-backend GitHub Wiki

Why we (still) use the Mercator projection

The world is a sphere. For transforming it’s three-dimensional surface on a flat 2D screen there is the need for a transformation. That is not seamingless possible. Imagine an orange that you peel and then carefully arrange the skin on the table as a coherrent form. You’ll have to deal with gaps, bucklings, wrinkles. You’ll need a concept and you have to deal with distortions.

Same goes for the task to project the world onto a map. One projection was invented by the geographer Gerardus Mercator in the 16th century. Even having some flaws, and not being complete, it was considered helpful for navigation, which made this projection very successful over the time. Navigation like in steering a ship from Europe to America or Africa. It was the time of conquering and colonizing.

The Mercator projection is very bad in representing land masses correctly. This distortion of land masses makes Africa and South Amercia drastically smaller, while parts of the north are over stretch and much larger. So the projection got criticism, for example in the 1970s. Like the historian and cartographer Arno Peters, who was critizing it’s Euro-centric perspective, that favors (enhances) the global north and minimizes the global south. He also proposed an alternative projection to overcome such distortions and to represent all land masses correctly.

But despite this Mercator made it as the de-facto standard for web-based maps until today. Again, because navigation works good with it and it displays the lines between two points straight. So most web-based mapping systems are based on the Mercator projection. But this starts to change a bit. In 2018, Google Maps changes the global perspective of their map to an „orthographic map projection“. So it is basically still a Mercator projection on city or state level, but it switches to an orthographic representation if you zoom out the map to an world-scale. In 2021, Mapbox, a commercial provider of tools and tilesets based on the free Openstreetmap map data, announced an update of their library with a similar and very promising move. Mapbox is commercial, since we want to create a map client, that is free of dependencies to commercial products or licences, we won’t use this solution.

There are open source tools, where you can choose from different projections, like the popular D3.js library. But with that you’d need a lot of extra work, to make a web map easy and smoothly working. There are specialized free webmap frameworks – like Openlayers or Leaflet (what we are using here) – , they are great and very handy, but none – a least to our knowledge – provide a way to use a different projection … yet. Surely this will change in the next time. Hopefully! Because we think, that it would be generally good to have the possibility to choose between different projections. That at least would force us to think about the meanings and hidden assertions those projections may take. And we would like to use a non-mercator projection (like the Eckert-IV projection) for our web maps!

If you have ideas, comments or hints on this topic, please share them with us! :) --> [email protected]

Ulf Treger, A thousand channels