The city of Melbourne, Australia did a study of various types of urban density (it’s a PDF) to inform their own planning for the development of the Southbank area. The study as presented here is a little bit cartoonish, but they do pull together various quantitative measures of different neighborhoods around the world, which are interesting to compare — from Hong Kong to Barcelona to Battery Park in NYC. Their conclusion: uniformly developed low-rise, 3-8 story buildings can produce as much density as anybody might want (tens of thousands of people per square mile, just look at Paris), and are more conducive to a livable urban environment than towers, and in fact many tower heavy districts aren’t all that dense in aggregate. Parking regulations are key to making good urban space for people, as is the provisioning of social infrastructure (common green space, libraries, good schools) within walking distance. They suggest that densities of 100 residents and 50 jobs per hectare (30,000 and 15,000 per square mile, respectively… wow) represent a threshold at which fully featured urban infrastructure (including public transit) can pay for themselves.