Tissot's Circles: Seeing the Warp

Here's a clever trick for seeing distortion instead of just being told about it: imagine drawing a tiny, perfect circle at every intersection on a globe's grid lines, all exactly the same size. Now project the globe onto a flat map and watch what happens to those circles.

On a map that keeps shapes true, like Mercator, the circles stay perfectly round everywhere, but they grow to wildly different sizes depending on where they are. Near the poles, a 'circle' the same true size as one at the equator gets projected many times bigger.

On a map that keeps size true, like Equal Earth, the circles all stay the exact same area as each other, but many of them get squashed into ellipses instead of staying round. The size is honest; the shape isn't.

The Distortion Lab lets you turn this grid of circles on over any map, plus a color heatmap of where distortion is worst. Flip between projections and watch where the 'trouble spots' move to — they never disappear, they just relocate.