In the past we have made cities because of economy of scale effects, and because we are social animals. In the very past we have made them because we do not have had effective quick enough transportation systems, for defense, water proximity etc.<p>Nowadays at the actual evolution state, at the actual needs the economy of scale effects do not happen in cities anymore but in Rivieras, witch differ from USA suburbs because they are not residential-only areas but a mix of residential and work areas, a bit dense but not too much to have no room for evolution, not too low do have no benefit of density scale. That's is.<p>In the very past when cities were little and made of rocks and wood changing them was moderately easy and normally happen after a <i>not infrequent</i> catastrophe, now with concrete thing have changed much, we can't "source raw materials where we are, recycling the past mess" and that's another important issue: we know concrete do not last forever and we made big stuff with it with no real plan on what to do when will be time to decommission them. We allow keeping up crappy things because of someone interests against all others and again no plan how to sort the issue out. That's why not USA in particular but essentially all other the world we can't build.<p>USA have showed and tested why differentiation fails: suburbs fails because they are residential-only, you need a car just to get a bottle of milk. Cities fails because of density. EU give even worse example of dense-cities issues. BUT all other the world we see that Rivieras keep going. Surely they are not universal, we can't made a mining industry with that model. We need some "districts" but some with a single purpose, a single owner, aside that we can a day erasing them and restart over.<p>Such model is <i>implicit</i> in the Green New Deal, even if people, even UN New Urban Agenda deny it, we can evolve single-family homes with a bit of land around, we can't for tall buildings and dense areas. IMVHO the Green New Deal also tell without telling their "solution": pushing poor in modern cities who happen to be like prisons, of small size to be manageable, and live few wealthy aside. I doubt such model can scale, I doubt such "separation" can work in nature though...