Unless local or you have a team that is led by locals don't sweep large urban districts unless you know every inch of area you are sweeping if you can find maitinance guys that work for the city even better the more you know about the area the better chances of clearing the area of undead. Cities are good when you know how to work the terrain if you have a means of silent travel at a high vantage (rooftops) use it don't go zombie stomping through the streets yelling orders. Learn military hand signals keep vocal communication minimum especially when in zombie infested areas if one hears you they all will. If you see a pile of dead zombies at a baricade you probably found a fortress with a well-trained sniper at the top. and for the love of the lord almighty don't try to sneak in you'll probably be killed once you get into that fence, your best bet is to walk away until daybreak and try to make contact if you want to.