Zombie Difficulty

[Kinsoku-Nyan]

I just started playing this game, and I'm not quite sure what zombie is what. Already in my first day of Pioneer mode, I happen to find some kind of..."Bloater"? It completely destroyed one of the gates in the starter fort, and I don't even have the necessary materials to rebuild it. At night, some kind of "Spitter" charges into the fort, and almost attacked me. I have to wait (and hide) inside the radio shack until the next day. Unfortunately, the spitter killed me, and I have to restart back to Day 1 (since it was my last save).

The whole point of this is simple: Do you think there should've been a difficulty zone? Like, if I step inside a city area, I'll encounter tougher zombies? Or if I head to a campsite, there's certain zombies, such as dogs?
At least, I know for a fact that the zombies around the starting fort should just be walking zombies. Should be great for new players to experience their confidence on other zombies in this game.