UN-Habitat prescribes an urban density rate of more than 150 inhabitants per hectare. Inspired by the model of the compact (European) city, whose paradigmatic example is Barcelona (171 inhab./he), the New Urban Agenda (UN-HABITAT, 2020) condemns the urban sprawl of North American cities as Atlanta (6 inhab./he). However, the document does not mention the low proportion of green areas per inhabitant in Barcelona, one of the smallest among European capitals, and local efforts to improve it.

Recent work by Swedish researchers (BERGHAUSER PONT et al, 2020), comparing three hundred articles worldwide, points to the fact that density and compactness are desirable from the point of view of economics and transport, but problematic under ecological/health aspects. If American urban expansion based mainly on single-family typologies is not desirable, neither is the high-density model of Barcelona without enough green space – the Goldilocks Principle or Sustainable Densities Proposition (SHLOMO, 2012).