Yeah, basically. (How much is the entire world in data?)But I think it can be done for less by implementing a system where the player does not need to download the entire world (like you said, it's too big) but needs to download only the country that his character is at the moment. If he flies on a plane (which would take a lot of money, so the character needs to be well established with good jobs) and goes to another country, just delete the previous country's map and replace it with the new country's.
Ah, ok.That sounds like fun.