This chapter was written by: Shlomo Angel, Yang Liu, Alex M. Blei, Patrick Lamson-Hall, Nicolás Galarza Sanchez, and Sara Arango-Franco
Cities grow in population and wealth; as they grow, they both densify and expand. As cities expand, they convert new areas on their rural peripheries to urban use and create new urban peripheries in the process, newly settled areas or newly annexed villages and towns that were for-merly on the outskirts of cities and are now contiguous with or engulfed by the city’s expanding urban footprint. These new urban peripheries are the focus of this chapter. Previous research, supported by a rigor-ous theoretical framework, has established an important empirical regularity that characterizes new urban peripheries: They typically have lower average densities. More generally, it has been shown in numerous studies that population densities decline as distance from the city centre increases and, hence, we can expect that as cities expand outwards and away from their older centres, newly built areas will be further away from areas built earlier and will thus have lower average densities as well. Unfortunately, beyond this important finding, very little is known about urban peripheries and particularly about the new urban peripheries, areas built or incorporated into the urban footprint in recent decades. In this chapter, which is discursive and non-technical in nature, we report on a number of recent findings that characterize the new urban peripheries the world over– in our case, areas added to cities between 1990 and 2014. The report is based on our analysis of sat-ellite imagery and census data in a stratified global sample of 200 cities, a 4.7 per cent sample of the universe of all 4,231 cities and metropolitan areas that had 100,000 people or more in 2010. We also report on a few additional findings from a pilot study now underway in ten cities in ten different world subregions.