Agricola, Sekigahara, Concordia, Innovation, COOKIE!!! (and Guinness)
SANJURO: You're all tough, then? GAMBLER: What? Kill me if you can! SANJURO: It'll hurt.
Probably a bit indirectly. It says that each player has certain amounts of tile-combinations in the setup description (page 6) The only way to place new districts is with the card actions. By exploring, or extending an existing place. (described in page 20)
Also note which way up the different cards place the districts! (Explorer vs. Mayor)
I agree it's there in the rules and the cards, but I also found it slightly confusing at first.