Cities or large urban areas have two differences in a major outbreak, living and dead. A dead city is a city completely overrun by the undead except for scattered survivors. Living cities are still operational and run by survivors.
These are,as previously mentioned, cities still controlled by the living, not the living dead. No one has ever written about these cities, or the categories and conditions of them. Therefore, do not discard the following information as it is the only of its kind and there are no famous or established authors writing about it. The categories of a living cities follow:
Red cities are in a very big mess. They have mild to moderate outbreaks every once in a while. Government is either non-existent with small bands of survivors ruling the streets, weak and unable to control the population and/or lacking the manpower to provide for them or tyrannical with selective people getting protected while others are left to fend for themselves.
Yellow cities are in better shape then red cities. Yellow cities have only mild outbreaks usually able to repel the hordes. They have a weaker government than most modern cities, but better than the feudal government or rampant anarchy red cities have. Yellow cities can produce small amounts of resources and a weak economic system is in place. Laws are made and a rudimentary police/military force may be in place to uphold it. Their food and water supply may be unsustainable but citizens of a yellow city will get a little of it at the very least. Electricity may be avaliable in selective areas.
Green cities are in good shape and have moderate governments and most likely will have power being independently generated. They have a decent agricultural system in place for producing food and may have water purification. They have a law system and the ability to utilise it, decent economic situation and defense against the undead. Little to no outbreaks, with the majority living a lower middle class life style.
Gold cities are where you want to be in a zombie controlled world. A operational government, electricity, sustainsable food and water, trading with other possible settlements, medical care and no outbreaks. Gold cities will take steps to liberate more land from zombies and begin repopulation. They will become a power in the post-apocalyptic world.
Setting up a Living city
Zombies have began to overrun towns, cities, states and countries. As the world you know is crumbling around you, you realize that in the sea of chaos, a secure settlement can protect you like a life boat. How you set up this life boat will be crucial to your survival. Banding the remaining inhabitants will definitely help. Co-operation allows your settlement to survive and thrive. Set up fortifications around a defensive perimeter. Make the size of the perimeter in proportion with your needs and defensive capabilities. Do NOT attempt to reinforce a location without the necessary manpower or resources. Construct a fence, trench or wall to keep the undead out, preferably multiple in case of breach. Now that the outside is dealt with, pool your resources, such as firearms, ammunition, food and clean water in the settlement.
Long term Survival
Very rarely will a living city survive on stored and stockpiled food. Even if you can successfully fortify a city, if you can not produce essentials to keep you alive, you might as well throw yourself to the living dead. Farming is a must. Rain catchers, and if on the coast, desalinization machines will be extraordinarily useful. Keeping the citizens fed is just as important as keeping them safe. Rescue, if it will ever come, shall take years. Until that day comes, you must be able to form a self sufficient community. America`s vast wealth is a result of vast resources, over even vaster lands. After zombies seize most of that land, you will find yourself a lot poorer. Remember, take advantage of every resource mother earth gives you, you will never regret it. If Your settlement had a lead or steel mine inside, get it operational. If you live on great farmland, farm; if you live on the cost of a river, lake or ocean, learn how to fish; if there a game reserve, hunt; if you have a gun and ammo factory, get it running. Take advantage of absolutely everything! You will also need an army or police force. Make sure it is loyal or well equipped, and loyal to the city.
Expanding the city
Methods to expand your territory are countless. The following are preferable:
Hold your fire till you see the whites of they`re eyes. Wait until the zombies come to you, kill them all, sweep the area and fortify it.
Frozen blood. Wait till all the zombies freeze, if you live above the snow line. Then make a defensive perimeter and wait for the thaw. Once it comes, sweep the fortified area until none remain.
Thinning ranks. Kill all the zombies within and around the settlement. Wait a month. If none or few arrive, send out a large posse of armed men. Have them sweep the area. If they find little to no zombies take the land and form another defensive position.
Dead cities/White zones
Overrun or abandoned cities, avoid them at all costs! Even if you think there may be supplies, loot and/or survivors, these areas be likely overrun by the undead as well as conventional hazards such as disease, collapsed buildings and roadblocks. If you are fleeing another outbreak it is always better to waste supplies traveling around the city than cutting through it. If for what ever reason you choose to disregard this advice then never travel at night, if possible move through the city between dawn and dusk. Do not stop for loot. The only time it is acceptable to enter a previously declared dead city, or White Zone, is after it has been declared safe, but even then always be on your guard. Some governments may find it advantageous to just nuke the city altogether (effective if there is only one overrun city).
Stay away from dead cities and try to get into live ones. A majority of cities will be dead, so don`t expect to find many of the live ones. Cities can be overrun and weak cities will get overrun easily. Always remember that living cities, especially Gold cities, will be heavily policed and protected. If you wish to gain access to a gold city, it would be worthwhile having something with you to trade for entry. The best items for trade are food supplies, medical supplies, and weaponry with ammunition. Another thing to consider when attempting to gain access to a gold city is what skills you or your team possesses. If you have someone such as a doctor or electrician with you, you have more chance of gaining access than, say, a musician or artist.