In urban planning, population density is a subject that sparks discussion, doubt, and debate. A common point of confusion, for instance, is conflating built density (the amount of built area in a given location) or even building height with population density (the number of residents in a given location).
In New York, for example, Midtown Manhattan has perhaps the city's highest concentration of skyscrapers, despite having a population density of "only" 18,000 residents/km²—less than half of the Upper West Side, which boasts 44,000 residents/km² with lower but predominantly residential buildings, whereas Midtown has fewer residential buildings. In Brazil, this discrepancy is far more extreme: the densest neighborhoods in major Brazilian cities tend to be the most horizontal, as they consist of informal settlements (favelas) with small housing units, minimal space between structures, and larger families living in (or cohabiting) these units.
