Putting on my most cynical/paranoid hat, I will say: If everyone lives in cities, and if the cities depend upon supplies trucked in from remote locations, then the government has a very easy time dealing with dissent. Absolutely any law can be imposed on the population, and what are the people going to do about it?? The day may come when we all live in the Warsaw Ghetto and crawl through sewers trying to bring back food from beyond the lines of an encircling army.
1) Government farms will produce the food for the subjugated urban masses.
2) Government transportation will supply these subjugated urban masses with government produced food.
3) Government agencies will decide which urban areas will receive what and how much government produced food.
4) Local governments, through their government appointed commissars, will decide which individuals will be allowed to receive government food.