I'm not sure I follow the population and density argument. City densities were higher in the 19th and early 20th centuries. Paris itself has lost about 700,000

I'm not sure I follow the population and density argument. City densities were higher in the 19th and early 20th centuries. Paris itself has lost about 700,000 people since its 1921 population peak. If housing people is your goal, you should build lots of low- to mid-rise buildings, say between 5 and 10 floors. This size of building is able to achieve the highest densities per cost using current construction techniques. Build lower and you over-allocate and waste land. Build higher and the marginal cost of another floor rises quickly. There's a reason commercial buildings are the tallest: workers need less space working than they do living at home. High-rise residences are not economical unless people have very small apartments, which brings along its own problems.