Episode 2: What is a projection?

The challenge of mapping.

In this article, I proposed a definition of what a map is: a flat representation of the terrestrial sphere.

And now it gets fun. Because it's impossible to represent the image drawn on a sphere flat without distorting its outline.

Projection by Bernard J. S. Cahill, digitized by Gene Keyes from the cover of a 1919 brochure, The Butterfly Map.

Try to imagine the world drawn on a grapefruit peel. With a clean incision, you can peel the orange while keeping the skin in one piece. Then, try to lay this yellow world flat on your table. Very quickly, it will turn into a mess.

This example is taken directly from the short video below. It perfectly illustrates the difficulty of this endeavor.

The Impossible Map by Evelyn Lambart, 1947

The cartographers' puzzles.

Inevitably, a whole host of people, often math or geography fans, began to rack their brains to find a solution to this problem.

Among the panoply of ideas that emerged from all these buzzing brains, three teams stand out.

The angles team.

These projections aim to maintain the same angle values on the globe as on the plane. Their idea is rather to preserve the shape of a country or a continent.

Mercator conformal projection, from the NASA Earth Observatory's "Blue Marble" series.

The surfaces team.

For these projections, the real challenge in life is not to make a country, for example, appear larger or smaller than it is. They therefore try to preserve as much as possible the areas of a region when it is transferred to the plane.

Lambert azimuthal equal-area projection, from the NASA Earth Observatory's "Blue Marble" series.

The "Let's-try-something" team.

These projections preserve neither angles nor surfaces, but try to approach a bit of everything at once.

Robinson aphylactic projection, from the NASA Earth Observatory's "Blue Marble" series.

I give you all the juicy details about the first team in this article.