Looking back at the Fallout 4 footage from Microsoft conference, and the Kotaku Script leaks, I've picked out a few locations and figured I'd show people where they are for people who want to learn more about the potential Map size, and its contents.
http://imgur.com/a/7p9t4
The following shows the areas; Concord, Lexington, Quincy, and a reference to what is speculated to be the location of the Glowing Sea, according to concept art shown in the E3 Footage, and nicely presented by a Redditor: https://www.reddit.com/r/Fallout/comments/3bc1sj/fallout_4_the_glowing_sea_details_from_the/
All this shows that we will at least have some of the Northen and Southern sides of Boston, I for one hope there is a decent amount of Rural areas to explore and live in as well. (I'm no City Kid)
Let me know your opinions, or any other information on the map you'd like to share here!