For a bit of context: <a href="https://en.wikipedia.org/wiki/Tissot%27s_indicatrix" rel="nofollow">https://en.wikipedia.org/wiki/Tissot%27s_indicatrix</a><p>This is an essential tool to teach, not only map projections, but the more general concept of Riemannian metrics!<p>See also the Dupin indicatrix, whose wikipedia article unfortunately lacks good figures: <a href="https://en.wikipedia.org/wiki/Dupin_indicatrix" rel="nofollow">https://en.wikipedia.org/wiki/Dupin_indicatrix</a> (it makes a funny appeal to "just imagine them"...)
Somewhat related (if you’re one of today’s lucky 10,000):<p><a href="https://xkcd.com/977/" rel="nofollow">https://xkcd.com/977/</a>
See also:<p><a href="https://observablehq.com/@d3/projection-comparison" rel="nofollow">https://observablehq.com/@d3/projection-comparison</a>