It is nebulous. But very much by design. Im certain the Toolkit will give some examples. But, this is certainly something that should be easier for Old-hats to pick-up than new DMs. Its strenght is in that it can be modified on the fly.
As a player you got just gatta run with it and trust your DM has the best interests of the party at hand (otherwise why are you playing with them).
As a DM, your goal is to prepetuate the game in favor of the players, so you jsut need to ensure consitancy. The Zone system may be difficult to grasp for “rule-lawyer” type players. but it allows you to repbalance as encounters are generated and doesnt require reliance on board visibility like say 3.5\PF
Side Note: I also just posted an ecounter map with a zone division in my HB topic ([Homebrew] Welcome to The Dominion - #9 by ComradeCannon)