A previous dev has suggested that the GTA 6 map really should be smaller and much more densely packed. Even so, as leaks have ongoing to trickle outside of Rockstar, modders have recreated the GTA six map in GTA 5's engine which offers a sense of its significant scale. https://gtasixreleasedate42075.ziblogs.com/35526090/everything-about-grand-theft-auto-6-website