The map in Fallout 3 is pathetically small, the locations are practically tripping over themselves. Fallout 4 should be made by a company compitent to handle Fallout, and it should include the entire http://en.wikipedia.org/wiki/BosWash. And it should have a car.
And since Bethesda loves subways so much, I'm sure they'd have a blast loading up the Northeast Corridor with mentally retarded Super Mutants, mentally retarded Deathclaw, and feral ghouls who apparently don't know how to use weapons or speak for no apparant reason.
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Yeah I was suprised about how small the map looked. Someone I think said it is the same 16sq mile playing field from Oblivion but it feels a lot smaller if it is. It'd take about 30 minutes to get through the northmost of Oblivion all the way down to the bottom. In Fallout 3 It takes about 20 or less minutes depending on the obstacles (and I think you run slower). There's subways all over the place in D.C. because...well It's D.C... and people move around...by the subway. I do admit though some of the "Underground tunnels/basemant" Halls are a lil bit bland if it weren't for the combat. I do appreciate the quests in Fallout a lot better though. They're more exciting or twisted compared to quest in some other games.
Anyways, Fallout 2 did have a car you could run off of micro fusion cell. a car would be interesting for a bigger map but considering the uneven and rocky wasteland it'd be a pain to drive an old 60's (or etc.) car on it. Though if some citizen npcs found a way to construct a jeep in a town or camp that a player can take, it could be possible. Plus considering the fast travel mechanic new to Fallout would basically render a car useless except for the more stubborn players (It took me awhile to use the fast travel systems until I started getting into a lot of quests. It also helps getting by all the streets covered in impassible rubble ^.^) .
Manhattan sounds like a good mixed environment for the team to get creative with. Supposedly it also gives a lil more breathing room. Note: I'd take the full 30sq miles if possible... Fallout did seem small in comparison to Oblivion.