When I first started out, I had this conception that the base setting of Apocalypse World was a "Mad Max"-style wasteland, and I rolled with that. In truth, the setting can be however you want to spin it. I ended up editing it to be a more temperate wasteland set in Paso Robles, using local landmarks as inspiration (I needed a plausible military base in proximity).
The AW book says to stay true to your research, but if the players improvise a setting detail on their own - a detail which may contradict something that you have technically already written down somewhere in your brainstorming, but have not yet shown "on screen" - then you are free to edit/replace/whatever and go with what the players suggest. The players' suggestion will ensure more investment in the setting, and you can possibly re-introduce your cool idea elsewhere.
That said: if you've already established an element of the fiction, then don't retroactively change it, unless circumstances make it feasible. Your NPCs are always in your crosshairs, someone can always start polluting the "clean" river nearby, and a faceless post-apocalyptic technology-hoarding enclave can always start releasing mutated spidercats into your players' neighborhood.
So, as to "I am Legend": I found many apocalyptic images online, and the ones which fascinated me most were the ones in large urban centers, with lots of tall buildings, much like the setting of "I am Legend". I am also a veteran of the "Fallout 3" and "Fallout: New Vegas" games, so I am experienced with the look and feel of traveling through sprawling urban wastelands. So many options for ecologies, environmental hazards, resources, territorial conflict, surprise attacks, and more.
So if I had to do it again, I would opt for a more urban setting for my Apocalypse World game, something with a lot of gutted office buildings or skyscrapers, something which would allow me to include a diverse array of locations: parks, buildings, subways, car-choked roadways, hospitals, factories, and more. I think your idea has a lot of possibilities.