For a bit of context: https://en.wikipedia.org/wiki/Tissot%27s_indicatrix https://en.wikipedia.org/wiki/Tissot%27s_indicatrix This is an essential tool to teac

For a bit of context: https://en.wikipedia.org/wiki/Tissot%27s_indicatrix https://en.wikipedia.org/wiki/Tissot%27s_indicatrix This is an essential tool to teach, not only map projections, but the more general concept of Riemannian metrics! See also the Dupin indicatrix, whose wikipedia article unfortunately lacks good figures: https://en.wikipedia.org/wiki/Dupin_indicatrix https://en.wikipedia.org/wiki/Dupin_indicatrix (it makes a funny appeal to "just imagine them"...)