A previous dev has prompt which the GTA 6 map needs to be scaled-down and much more densely packed. Even so, as leaks have ongoing to trickle outside of Rockstar, modders have recreated the GTA 6 map in GTA 5's engine which gives a sense of its large scale. https://gtasixdownload86317.blogocial.com/5-essential-elements-for-grand-theft-auto-6-ps5-71125342