I find the cities = death part interesting; the show is stressing that those that survived were the ones that got out of the cities. They seem to believe that outside of the cities there is plenty of water, food and space just sitting there ready to be claimed by any who would make the trek (at least that's what's said through the Mom in the flashback).

This seems to be a popular idea, that in a major, nationwide disaster you could just head out of town with minimal supplies and find/take whatever you need.

Makes me think that if anything were to happen, maybe the cities will be the safest place after all .