Oh to those who are curious how my system works:
ZSpawn v1.0
Does a random check of a variable to decide whether to spawn something or not.
Checks if there's more than 30 zombies.
Checks if a zombie spawn is within a certain radius.
If so then it spawns zombie.
!?!?!
Repeat.
Basicly it spawns zombies off screen but not too far away and caps zombie count at 30.