Would this be possible?

[lovkal 242]

Would it be possible to create the entirety of London in its full size as a map mod for GTA IV?

Or are there map limitations to memory or the CPU, etc?

[LCPD_OFFICER 30]

There might be a problem with missions and AI path, if you keep it to low poly buildings you MIGHT make it if it's as large as iv's original map

[JASONROCKS1998 80]

Would it be possible to create the entirety of London in its full size as a map mod for GTA IV?

Or are there map limitations to memory or the CPU, etc?

Most likely no. The reason NY works is because it was done by R* professionally and it was scaled down. London at full size would most likely not work and would definitely crash a lot. Everything would have to be redone, including mission starts, LCPDFR locations and all that. Closest you'll get is proper road markings and traffic and the like.

[Illusionyary 4,632]

The entire of London to scale? No, definitely not. You could probably recreate parts of it but it'd still be a mammoth job and I doubt anyone will undertake it anytime soon if at-all.