Charles Dupin

Pierre Charles François Dupin (October 6, 1784, Varzy, Nièvre – January 18, 1873, Paris, France) was a French Catholic mathematician. He studied geometry with Monge at the École Polytechnique and then became a naval engineer. In 1819 he was appointed professor at the Conservatoire des Arts et Métiers; he kept this post until 1854. In 1822, he was elected a foreign member of the Royal Swedish Academy of Sciences.

In 1826 he published a thematic map showing the distribution of illiteracy in France, using shadings (from black to white), the first known instance of what is called a choropleth map today.

In addition, he had a political career and was appointed to the Senate in 1852. His mathematical work was in descriptive and differential geometry. He was the discoverer of conjugate tangents to a point on a surface and of the Dupin indicatrix.