It's one of the things any writer decides almost at the beginning. Where does my story take place? In a familiar location? In another country? On another planet? Is it taking place now? In the future? In the past? Some stories can take place anywhere; some can only take place in a specific location. How big a role do settings play?
In the case of my current WIP, this story could only take place at this location. I couldn't move it to another country, nor could I move it to another time in history. Some of the plots depend on it. It's just the way it is. It is frustrating sometimes that I can't get in my car and drive there, but I'm compensating with pictures from internet sites, period travel literature and my own memories of being in that general part of the country. I wish I could write books that could happily be placed in my own backyard (so to speak) and in my own time. Ah, well; I shall put it down to one of life's little jests.
In some books, settings are background and nothing else. The same story could be picked up and placed (for instance) in any large city or any small town. A tale of a young woman finding the love of her life (and really good shoes) doesn't have to take place in New York or London. Breathlessly paced political thrillers don't have to be set in national capitols, but it certainly helps up the ante. Let's face it, the ramifications of trouble at the White House or Whitehall are more dire than the spectre of trouble at City Hall.
Then there are the settings that lend themselves to certain types of characters. There's not a large number of moonshine-brewin', tobacco spittin' types walking around Wall Street (or if there are, they're very well disguised). Granny isn't going to be sitting on the porch, sipping a mint julip, in Paris. If you need these characters then you have to give them their setting, whether you actually can get there or not.
Did your plot dictate your setting, or did your setting dictate your plot? Do you have a character that only works in one type of setting? Is your setting simply the background for your story or is it a character by itself?