Metropolitan areas in the world. Delineation and population trends

This paper presents a novel method to delineate metropolitan areas - or functional urban areas (FUAs) - in the entire world and assesses their population trends. According to the definition developed by the OECD and the European Union, FUAs are composed of high-density urban centres with at least 50 thousand people plus their surrounding commuting zones. The latter represent the urban centres' areas of influence in terms of labour market flows. The proposed method combines a functional and a morphological approach to overcome the dependency on travel-to-work data to define commuting zones and allow a global delineation. It relies on a probabilistic approach and the use of population and travel impedance gridded data across the globe. Results show that around 3.9 billion people, making up 53% of the world population, live in 8,790 FUAs, out of which 17% live in their commuting zones. Between 2000 and 2015, population growth was higher in larger FUAs, highlighting a general trend toward higher concentration of the metropolitan population. Commuting zones grew faster than urban centres, though with heterogeneous patterns across world regions, income levels and metropolitan size.