I agree. The more densely packed an area, the worse it will be. But city survivors will move out to the suburbs and then the country in search of food as their current sources run out. And that won't take very long. I think they say that most grocery stores only have a 3 day supply. But they'll be wiped out much faster than that. The shelves will be stripped in hours once people realize the severity of the situation.
I've read it. "One Second After", "Patriots". There are a number of good fictional materials for those interested. Lets just hope it remains fictional.