A former dev has advised the GTA six map must be lesser and much more densely packed. On the other hand, as leaks have ongoing to trickle outside of Rockstar, modders have recreated the GTA six map in GTA five's engine which offers a sense of its large scale. https://gta-six21863.ourcodeblog.com/35589978/grand-theft-auto-6-release-no-further-a-mystery