More like 4. RBY & GSC, RSE, DPP, BWG?
So Saffron City, Sootopolis City, Spear Pillar/Distortion World, N's Castle.
I'm not talking regions. I'm talking time periods. The happenins of RBY and RSE happened all at once. The Giovanni, and the Magma and Aqua leaders all lived at the same time.
Then GSC, and DPPt. happened. Silver battled Gold at the same time his rumored older sister Jupiter aided Cyrus in battling Lucas.
LASTLY, we have BW, which happened in the "American" region of the Pokemon world that has pretty much no connections to the other places, minus people like Cynthia. (Notice she's been alive since DPPt and Kaitlin is OLDER, but not much older) We can assume time passed between BW and DPPt/GSC, but not much. Kaitlin is still young when she becomes an elite four, and Cynthia doesn't look too old.
I figure some major places for the time periods would be:
Indago platue or Battle of Origin
Sinjo Ruins, or Spear pillar
N's Castle or Dragonspiral tower (I think that's what it's called)