In reply to d_b:
There are a few other glitches. If you try and put the earth onto a nice flat grid, it doesn't really work, so you have a crumple a few bits up to pretend you've got a nice regular system. One of these points happens to be smack in the Kuwaiti oil fields - a patch of desert presumable dismissed as unimportant when the crumpling was being done. However, come the early 1990's things were rather different. I consequently found myself standing next to a few burning oils wells, wondering how my then new and shiny Magellan GPS reckoned that the next point of interest was over 17kms away, when I was certain it was only 3kms. A close look at the map showed a converging mess of grid lines. I set off, watching the GPS with interest: as it got to the mess of grid lines, it mentally disembowelled itself, did some big sums, and failed to come up with a sensible answer until we emerged from the mess, at which point it proudly declared that the said point of interest was just over there.