Comment by patio11

This is essentially the same as a traditional animated movie: gigantic sum of work to do, essentially infinitely parallel, and capable of being process-optimized such that two adjacent frames require much less work than freehanding them. They're probably using a large library of templated buildings (how many silhouettes are there at that resolution, really?), brushes, and then just applying detail work to the significant ones.

It's a big job, and it's impressive, but it isn't "We had enough people to freehand a scale map of the entire country, bwahaha."