Q&A: One Question, many locatons

I have always wanted to create a site that allowed one question to be answered by many but separated by location (i.e. city or zip). Can anyone help be brainstorm this idea into fruition? I am guessing I need to get a database of cities/states or zip/city/state, and incorporate the location into the user's profile. That sounds hard in itself, but I have never really built something like this before. Then, I would need to separate the answers so they are only visible if you are viewing a specific location within the database. Any thoughts?