Conformal map

In cartography, a map projection is called conformal if it preserves the angles at all but a finite number of points. Examples include the Mercator projection and the stereographic projection. It is impossible for a map projection to be both conformal and equal-area[?].

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In complex analysis, a conformal map is a function f : U -> C (where U is an open subset of the complex numbers C) which maintains angles, and therefore the shape of small figures. A function f is conformal if and only if it is holomorphic and its derivative is everywhere non-zero.

(In other words, "conformal" means the almost same thing in cartography that it means in complex analysis.)

An important statement about conformal maps is the Riemann mapping theorem.