[dclecbyo] 20 centers of projection

assume a map projection in which distortion is small near the center of projection and large toward the edges, e.g., orthographic.  depict a sphere as a collection of 12 or 20 maps centered at the vertices of an icosahedron or dodecahedron respectively.  the maps will overlap, perhaps by a lot.

12 = 3*4 and 20 = 4*5, so both numbers are good for putting the maps in an elegant rectangular array.  if one avoids placing centers of projection at the poles, north can always be up.

with 20 centers of protection, the distance between adjacent centers is about 42 degrees, 2900 miles, or 4700 km, a surprisingly large distance.