The dynamics of global urban expansion

TLDR

The study investigates global urban expansion by defining a universe of 3,943 cities over 100,000 residents and selecting a stratified sample of 120 cities. The authors analyzed decade‑spaced population data and satellite imagery for 90 of the 120 sampled cities, computed built‑up area, density, compactness, and contiguity metrics, and constructed ten econometric models to explain and test neoclassical urban expansion theories. The study concludes that developing‑country cities should adopt realistic, minimal expansion plans, allocate sufficient land, invest in core infrastructure, and safeguard sensitive areas to manage growth.

Abstract

This study examined the dynamics of global urban expansion by defining a new universe of 3,943 cities with population in excess of 100,000 and drawing a stratified global sample of 120 cities from this universe. Population data and satellite images for two time periods - a decade apart - were obtained and analyzed, and several measures of urban extent and expansion - among them the built-up area of cities and the average density of the built-up area - were calculated. Data for 90 cities out of the global sample of 120 is presented and analyzed in this report. Weighted averages of the built-up area and the average density, as well as compactness and contiguity measures-and their change over time-are presented for nine regions, four income groups and four city size groups covering the entire globe. Ten econometric models that sought to explain the variation in urban extent and expansion in the universe of cities were constructed, and several hypotheses postulated by neoclassical theories of urban spatial structure were tested. The policy implications of the analysis are presented and discussed. The central message of this study is quite clear: Developing country cities should be making realistic-yet minimal-plans for urban expansion, designating adequate areas for accommodating the projected expansion, investing wisely in basic trunk infrastructure to serve this expansion, and protecting sensitive land from incursion by new urban development.