Thanks for the explanation.
Given two cases, one with single-family homes spread out in a rural environment and a 7 story apartment building, the apt building may fare better in a zombie apocalypse because you can defend it easier (assuming zombies can’t climb walls). Approaches are limited, and incoming sight lines are short. Stairwells are built-in choke points.
The rural area, though, has a perimeter problem that’s difficult. Even if you group families together, the rural home has no stairwells to defend and lots of entry points, and lots of horizon to watch.
Seven or eight zombies with radios engaging from 300 yards would be a tough problem to solve.
So the vulnerability map needs a little modification, since while it does cover flood and weather and civil unrest, it does not include zombies.
The Center for Disease Control looked at the zombie problem:
http://www.cdc.gov/phpr/zombies.htm
As did Hornady:
http://www.hornady.com/ammunition/zombiemax