Depending on backstory and lore, I think the map should be have a layout as follows:
Here is the major radioactive zone. Abandoned buildings loaded with resources and treasure, zombies by the dozen, and heavy radiation. Full rad suit recommended for exploration.
Slightly less radioactive. Zombie ridden, though not as heavily as the city center. Abandoned buildings loaded with resources. Rad suit recommended but not necessarily required.
Even less radioactive zone. Small abandoned houses can be found here, plop a door on it and call it home, or build nearby if it is already taken. Watch out for zombies hiding in houses, they might get the drop on you. Few resources found here.
Furthest “circle” outside of the city. Not irradiated, or radiated in very small patches. Animal-heavy, lots of trees and rocks, perfect for harvesting. Also ideal for building. Not very many abandoned buildings or zombies, but you will find stragglers out here.
Mountains, Streams, Valleys, and Everything Else
All other zones are found farther out, or sporadically found in other zones. Less life found on mountains, but more rock/tree resources, lots of animal life near streams, and valleys are a good gathering place for both. Any other sort of land would fare similarly or differently depending on extremeness of climate and terrain.