my opinion

I think we’ll eventually see a reversal of the 200-year-long cycle of people moving from farms and small towns to big cities. Food production is going to be a big problem when oil-and-gas-based agriculture is no longer possible, and we will have to reestablish a more meaningful relationship between urban places and a more productive agricultural land. (We will have to get much more of our food locally in the decades ahead.)
Our mega-cities will contract substantially. The fortunate ones will densify around their old cores and waterfronts — though sea level rise may affect many harbor cities. This process of contraction is likely to be problematic and disorderly. In America, there is certainly the potential for ethnic conflict.
Categorically, our colossalProcess will not be sustainable in a post-oil future — and despite the wishes and yearnings of many people, the truth is that no combination of alternative fuels will permit us to continue living at this scale. Some of our cities will not make it. Phoenix, Tucson, and other Sunbelt cities will dry up and blow away. In Las Vegas, the excitement will be over. Other mega-cities will have to downscale or face extreme dysfunction, New York ecitement will be flushed away. One thing that almost nobody is paying attention to: the skyscraper will not be a viable building type in our energy-scarce future. Six or seven stories must be the practical limit in a new age when electric supply is not necessarily as reliable as it has been in our time. Cities overburdened with mega-structures will have a severe liability.
The suburbs, for the most part, are toast. They have three possible outcomes in the twenty-first century: as slums, salvage yards, or ruins.