A previous dev has suggested that the GTA 6 map really should be smaller and even more densely packed. Even so, as leaks have ongoing to trickle outside of Rockstar, modders have recreated the GTA six map in GTA five's engine which provides a sense of its enormous scale. https://zionyxtsp.total-blog.com/indicators-on-grand-theft-auto-6-pre-order-you-should-know-61572829