Urban scaling theory: Answers to frequent questions

Since its start about 15 years ago, urban scaling research has become a vibrant component of the emerging field of urban science. Initially, this work focused on the identification of nonlinear relationships in urban quantities relative to population size, but more recently it has expanded to include efforts to explain observed scaling relationships in terms of new theory. We find that some misunderstandings have arisen in the literature concerning the nature and purpose of this work. Here, we address several persistent questions that have been raised with respect to urban scaling theory, clarify what we perceive to be its achievements and distinctiveness, and highlight questions and areas of opportunity for future work.