What are you going to do once the undead rise?

[Philly Mike]

Island = easier to defend, the zombies can only come from the land mass side, they can't come from the ocean, and anyone who displays any zombie tendencies we already decided would be shot on the spot.

but what would you do if you reach land and there is already a huge swarm of zombie waiting everywhere you can possibly make landfall?
You at least have more security if people band together and you build fortification and countermeasures, instead of uprooting and taking chances on trying to settle somewhere that is a true unknown. you run the risk of going there only to have to turn back and maybe not have a place to turn back to.