That's what "full" means in practical terms. Obviously the parent doesn't mean "the entire city is a contiguous matrix of one-cubic-meter boxes, each with a person inside". People will have different opinions on whether it's "full", of course, based on how much they are willing to fundamentally alter the nature of the location, traffic, desirability, etc.

This is true of every location, of course. Major metros are just where the population, and acceptance of density, is highest, so it's the obvious example to look at.