Some other issues people have brought up like beamng's size limit aren't really relevant here assuming you're just porting the model, since you wouldn't use beamng terrain for that. If you want to get a sense of scale, every single object that can be knocked over with a car is it's own object so you would need to find it's model (most likely shared with another but doesn't make it much easier) and get it's coordinates to enter into blender or the world editor depending on where you're arranging it all. if you want to do the full thing this also assumes beamng has no limit on the number of objects and that even with full lods the game will be able to run it reasonably. The best starting point to discover driving. This means that for every one of the hundreds of thousands of props, you need to convert it, it's textures, it's lods, write up a beanng materials file for it and then get it's coordinates from the gta map and into the beamng world editor. Want to play Driving Games Play Burnout Drift: Hilltop, Cars Thief, City Rider and many more for free on Poki. The map itself is comprises of hundreds of thousands of models, every single one of which, in it's model, is centred.
I've been looking into porting it for a while but the full thing will literally never happen
