The "easiest" way to handle a "torus" world would simply be to ignore any 2D distortion caused by contorting it in the 3:rd dimension (hence my quotes). On the embark map you'd just continue over the edges (possibly with some kind of indication of the starting "frame" around the world). That kind of thing ought to be possible within the framework of the myth & magic release handling of multiple planes, if desired.
Displaced tiles or whatever makes it awkward to navigate for the player and a total pain internally (and DFHack) to handle a new coordinate system. Even just using hexes, which is fairly common in games, would still mess up the internals badly.
When it comes to scales, I've seem a few of those:
- 16 * 16 world tiles for features
- 7 * 7 world tiles for "nearby" biome creatures
- 3 * 3 world tiles for region info
- 16 * 16 region tiles per world tile (called embark tiles by Max)
- 3 * 3 tiles per region tile for various features, including "local features" (they don't cross these boundaries, currently). I've got no name for these.
- 48 * 48 embark tiles (in my terminology, dwarf scale in Max') per region tile.
An official terminology would certainly be helpful.