Campinas / Atibaia
Also if the survivors enter all the buildings during the blue stage, it can't get any harder within the buildings later (since it's all spawned)
This will not always work out..
if just run and open every building at blue, none of you probably get a descent equip nor skill, and the amount of the Zs is not that low... you soon or later will be trapped with more Zs than you can deal...
depending of the scenario of course, but... usually this not worked as good as you suppose..