It's probably Gabe Newell in the background with a crowbar, signifying the imminent release of Half Life 3.

Damn Right!?

Interesting. Has any one noticed that the last few Bethesda games started you off roughly in the middle of the map? You think they would start us off in this game at the top left corner? Why would they do that I wonder? To force you in one direction?

In my estimation, in terms of what would actually be visible from the top of the vault area, the map may even extend as far North-West as https://www.google.co.uk/maps/place/Littleton,+MA,+USA/@42.5383056,-71.4852615,19156m/data=http://forums.bethsoft.com/topic/1526782-the-backround-behind-you-when-you-come-out/!3m1!1e3!4m2!3m1!1s0x89e3942d2a753711:0x753a4cc2a9138a64. This town does has some significance regarding the Revolutionary War, and would therefore be quite fitting as an'outer marker'.

But looking at the starting area, everything from the vault, the protagonist's home, the garage, the Museum of Freedom, and Concord itself appears to run roughly in a South-Easterly direction. This would signify that 1. all of these events are actually very close together in terms of when they occur, and 2. if this is all an 'extension' of the tutorial leading into open world gameplay, then the overall map size is likely to be enormous.

My own feeling (as per http://www.gamesas.com/topic/1526246-the-glowing-sea thread) is that the map also extends right into Boston Harbor and features extensive underwater exploration. Note that the two extremes of 'confirmed' locations, which are the National Park with the Minute Man Monument, and Logan International Airport, are actually 20 miles apart. If we then take into account the town of Littleton as mentioned above, as well as the harbor itself, then this distance literally doubles.