D3’s geographic projections allow features to be rotated about three axes. The three angles used are called Euler angles, and in D3 they specify the following sequence of rotations: This sequence is convenient, since if we approximate the globe as a sphere, the first two angles can be used to specify a central meridian λ0 and central meridian φ0 by simple negation: [-λ0, -φ0], and the third angle