I think most would be surprised to find that cities are not as impossible to survive in. I have done an E&E exercise in the city and found plenty of potable water not from the city. I found plenty of food growing everywhere including Corn, berries, plums, apples, and there is an abundant supply of protien running around.

Anyone that has ever been in the woods on the first day of hunting season will know there are a lot of people up there. Most people planning to run for the hills don't hunt. Still the rural areas are better for resources but the city is not at all as bad as most might think. You can find the most important things necessary for survival as they are far more readily available in the city. You can provide security and shelter far easier in the city than in the woods. There are pros and cons to both but having actually had to survive in a non permissive zone of the city it's not even close to as artificial as most might think.

I recomend anyone that ever travels to the city to take an Urban E&E class. You will be far more prepared to survive conflict.