A geodesic grid (http://en.wikipedia....i/Geodesic_grid) is my favorite way to set up grid on a planet surface. It has some nice properties for simulations, as it's basically what you need to use to make a hex grid on a sphere. (For a game where you just want to run around, a cube stretched into a sphere is fine).

The well-known Euler characteristic V - E + F = 2 for a 2-sphere absolutely guarantees that a closed tesselation cannot consist entirely of hexagons, but close enough. ;) Sorry for reviving other dead threads, I see what you were getting at now.

Hmm, I thought of one possibility that would be easy for designing maps, but I think a pain for converting to 3D. I started by thinking of the way games like Asteroids worked, e.g. you go off the left side of the screen and appear on the right. The toroidal mapping I guess that would be. So that's your level one approximation. The level two approximation would be having different numbers of tiles horizontally for each y position. Whenever you step off an "edge" you wrap around. On the equator you could travel east/west more tiles that in the north or the south. So the designer would work totally in rectangular tiles in 2D that can be traversed infinitely in any direction, but fancy footwork would be needed to map tile coordinates to screen coordinates to accommodate the wraparound.