You kidding? Liberty City is WAY smaller than San Andreas was. About one third the size, probably smaller. Assuming this is a recreation of the original, with no additional cities added on, it should be about the same size as the original, albeit with much more interior room.
Someone from Rockstar said in an interview a while ago that it was their goal to make the environment much more compact, as they felt San Andreas was too spread out to move around easily. I can't say I feel the same way, but that doesn't change what Rockstar is going to do.