I know that it has been a while since I updated this blog, but real life intrudes at the most inopportune times.
On with the show.
Since we've take a look at the big picture for what we want to do with our post apocalyptic geography (though without deciding on any changes), let's move on to building the initial setting base. Unlike fantasy genres where one can choose a top-down or bottom-up approach based on one's needs, some thoughts about the overall setting you want to go with means a more top-down approach has to be used when creating a post-apocalyptic setting. This doesn't mean you have to plan out your whole world or even a large area for a campaign. Rather, you need to consider three basic factors overall when designing your PA setting.
1) What was the place like before the apocalypse.
2) What type of apocalypse occurred.
3) When does your campaign take place in relation to the apocalypse.
When deciding what your setting was like prior to the apocalypse*, you need to consider essentially what the "tech levels" were. Early PA fiction didn't have many of the technological advances or research results that have been currently achieved, so they were both limited and less restriced in what they could do. Certainly that's a contradiction, however, both are true and stem from the same point; that is they were limited in knowing what kind of technology would be available, and unrestricted in what technologies they could imagine for use in their setting. This makes for some interesting thought with regards to retro-futuristic settings, such as the Fallout series, but also throws some limits in design based on how technology has progressed. For instance, a Fallout-like setting would see different technologies still possible, such as "ray guns" and "rocket ships", but would also suffer from the lack of new concepts that can be imagined from today's technology, such as "spider goats" or "carbon nanotubes". On the other hand, going with today's technological level means a loss of certain discredited ideas, such as "jet packs" or "mutants created by radiation." Of course, much of this depends on whether or not you go with the Low PA or High PA approach.
What you really need to know about the pre-apocalypse boils down to have available in your current setting; weapons, armor, medicine, food, water, fuel, and what is in ruins because of the apocalypse.
*Note: I use the term apocalypse because this is primarily considered a post-apocalyptic genre, the actual term used in a personal campaign or setting can vary widely, from apocalypse, End, Big Death, Crash, Armageddon, Ragnarok, the Fall, the Collapse, cataclysm, devastation, Great Destruction, holocaust, End of the Age, End of the Era, Fall of the Ancients, Judgement Day, Day of Reckoning, the Revelation, the Final Battle, The Big One, The Day the Music Died, the Great Bang, the Big Crunch, the Last Whimper, the Final Shriek, the Final Chapter, the Day of Judgement, the Tribulation, the Invasion, the Great Extinction, the Day After, the Pandemic, the Plague, the Disease, the Pestilence, the Epidemic, the Sickness, the Contagion, the Malady, the Curse, the Scourge, the Earth-Shattering Kaboom, etc.
The type of apocalypse that occurred, I've covered in my previous post. What this lets you cover is more on what happened after (or during) the apocalypse that made things the way they are now.
Determining when after the apocalypse your campaign/setting takes place, is the last macro topic you need to think about. I've seen a definition of 'post apocalyptic genre' somewhere that can be summarized into breaking the term down into two basic parts. One the current period is immediately after the apocalypse, that is, the apocalypse has occurred in living memory (even if it's only a few old farts clinging to life). The other period is where the apocalypse happened so far back that it, and the time before it are shrouded in myths and legends. In the former situation, survival and rebuilding civilization tend to take precedence in the setting. In the latter, exploration and discovery take on a stronger role.