The "Enemy Spawning" option allows the player to determine whether hostile creatures are to be placed in the game scenario. The higher it is, more creatures will be spawned in the scenario. By disabling Enemy Spawning in a world, one could explore the map as it is, without the time taking threat of zombies.
Disabling "Enemy Spawning" actually will not completely prevent zombies from spawning inside the game world; this is likely due to a bug. Common places for zombies to continue to spawn is in the Police Station and along the borders of a Biome.
Enemies will also continue to spawn when summoned by the car alarm of a Police Car.