I´m doing some research as to what the engine can do. While I do know that the engine can do these things because other games already have this, I just wonder how it is done.

Being a fan of RPG´s like Mass Effect and open world games such as GTA (but recently more Saints Row), I wonder how you can create open worlds. The most obvious solution would be streaming levels (probably the only solution for a world like Liberty City or Steelport) and it most likely already has been done in Wheelman.

I wonder with the problems a lot of people are having or the limitations by reading about level streaming on the forum or UDN how this works in a world such as in Wheelman.

So, for a more specific question: what are the actual limitations of level streaming and how big can one streaming level be before the game lags when loading it.

I also wonder as to how large distances are being done (such as skyscrapers and mountains) since these should appear normal when you approach them. Low-poly might work but how are those set up to seamlessly switch to the detailed level when you approach them; just create more LOD's? I do know to use modular pieces to create buildings, so no-one has to come with that.

I'm sorry if it isn't clear, but I've written this pretty fast, so feel free to criticize.