Not to mention, F4 is not the Mojave desert or the remains of a totally nuked DC. It is also not a medieval Scandinavian like province that is mostly wilderness.
It is the 200 year old remains of the greater Boston area that was left nearly untouched by the Great War.
The population mostly didn't survive the aftermath of the Great War, but it has to be one of the least damaged urban areas in the remains of the USA.
Add in that with the vertibird and jumpjets, we will be able to go places we never could have gone in previous Fallout and Elder Scroll games, and we are talking some serious verticality.
So what ever the scale it will still be one of the densest maps Bethesda has ever done.