[dchftcs]

Factories are themselves dense in resource usage, so it's different. It's a matter of scale.

A suburban neighborhood that hosts a few dozens of families requires more infrastructure, but can be replaced by a single 10 to 20-story building. An large apartment complex can serve hundreds of families.

Now, it doesn't have to be a dichotomy. It should be even more cost effective to build tall apartment buildings in the suburbs near the city. City-nations tend to expand capacity by creating new towns in suburban areas and extensive planning. That's much more efficient than US-style suburban sprawl.