For example, if you look at all of the periodic scales that you can get with the 25/24 and 81/80 chromas, you'll find that you get 49 different scales. If we consider scales which are modally equivalent to be in the same dome, then the playing field reduces to seven domes obtainable from the 25/24 and 81/80 Fokker arena. Each dome of this arena is a collection of seven periodic scales which are modally equivalent, which is to say, rotations of each other. However, every dome is independent from every other dome of the arena; the domes partition the set of scales of the arena into disjoint sets.
While we've defined a dome as a set, it should be noted it has a natural cyclic group structure.