PT - JOURNAL ARTICLE
AU - Bettencourt, Luis M. A.
TI - Urban growth and the emergent statistics of cities
AID - 10.1126/sciadv.aat8812
DP - 2020 Aug 01
TA - Science Advances
PG - eaat8812
VI - 6
IP - 34
4099 - http://advances.sciencemag.org/content/6/34/eaat8812.short
4100 - http://advances.sciencemag.org/content/6/34/eaat8812.full
SO - Sci Adv2020 Aug 01; 6
AB - Urban theory models cities as spatial equilibria to derive their aggregate properties as functions of extensive variables, such as population size. However, this assumption seems at odds with citiesâ€™ most interesting properties as engines of fast and variable processes of growth and change. Here, we build a general statistical dynamics of cities across scales, from single agents to entire urban systems. We include agentsâ€™ strategic behavior to produce predictable growth rates, which requires balancing relative incomes and costs over time. We implement these dynamics using stochastic differential equations and control theory to demonstrate a number of general emergent properties of cities deriving from limit theorems applied to growth rates. This framework establishes necessary conditions for scaling to be conserved by urban dynamics and shows how exponent corrections can be calculated. These ideas are tested using stochastic simulations and a long timeseries for 382 US Metropolitan Areas over nearly five decades.