I think I do tend to consider major settings as being almost characters in their own right, simply because they influence so much about the behaviours of other characters. Having lived in what was effectively an industry town for eight years (Canberra, Australia, where the major industry is the Australian Federal Public Service, and just about everyone there either works for the government, or works with people who work for the government, or knows someone who does either of those) I know the effect of a single large employer on the social and political landscape of a town or city. It distorts things, and the corporate personality of the employer seeps into the planning, into the structures.