You will have the opportunity to make your preference known.  Depending on the number of applicants, the needs of the region and the existing team sizes, applicants will more than likely receive placement in one of their preferred cities.  Likewise, the people who work on placement try to honor the request to be with a certain person.  The placement team is concerned with the well-being of each STINTer and will do their best to place each person in “the best” surroundings.