Disclaimer before writing my next post. Brockton Bay's location in the real world is never mentioned. However, I am relatively certain that they asked for help from Boston during the Endbringer attack nearby, so my headcanon says the two are close. 

Also, after the battle has concluded, I plan to write the first Interlude-style backstory reveal for one of the characters. Each player gets a vote as to which one I do, the one with the highest votes wins =P