...about the city on t... "Inverted World", I think. Author: Priest, or Priestly, or something like that.

Anyway... city was on tracks and must be kept moving. So it was a constant project to pull up the tracks in back and install them in front.

the geometry of the planet was inverted so it was shaped like the shape created by 4 hyperbolae, arranged in quadrants, and rotated about a north/south axis. This caused a north/south spindle with a disk shaped equator. Tips of the spindle and edges of the disk went to infinity, or something like that.

The reason they had to keep moving was that there was constant slow movement of the terrain towards the equator. And the city did not share the warped geometry. They had to stay in the curve closest to the center of the planet because that was where their geometry matched the geometry of the planet. If they let the slippage carry them towards the equator, the natives became short and squat. And there were centrifical forces that increased exponentially.

And there were time effects too (this is the reason your post triggered this memory). Time sped up when you moved more towards the spindle and slowed when you went towards the disk of the equator (or vice versa, I can't remember for sure).

Cool, wierd book.