N. K. Jemisin - "The City We Are (Great Cities Trilogy)"

Written wonderfully and I'm quite enjoying it. One thing that currently slightly irks me is the wishy-washy description of power and city-ness. There's multiverses. Sure. Cities squash through planes. Okay. Cities have power, and the Enemy can't fight them after they are born, but can stop the birth from happening. Okay. But where do they get their power from. What are the rules? Currently it seems the moment one of the boroughs, Aislyn (State Island), Bronca (the Bronx), Brooklyn, Manny (Manhatten), Padmima (Queens) "tap" into their power, they can just expel the Enemy. Is it that easy? I wonder if we will learn more of the rules, the backdrop, those infinite planes and multiverses (why do born cities squash through thousands of planes?) and I hope we get a deeper glimpse of the characters of each of these people.