I think there must be lots of people still out there, in bunkers and various protected locations. We haven't even begun to scratch the surface of that.
When Lori and Rick were talking about their abortive trip to the Grand Canyon, it occurred to me that that might not be a bad idea. Head for someplace that had low population density, like Arizona or Utah. The desert might be problematic in terms of water, but at least it's fairly warm. Coastal areas would have the best weather and water supply, but too many damn zombies.