Urban Expansion in a Global Sample of Cities, 1990 – 2014

Using a 200-city sample that was carefully selected to represent the universe of 4,231 cities in in 2010, we generated measures of cities’ areas and populations at three points in time over a 24-year period. The 600 observations were used to calculate the growth rates of cities’ areas, or their urban extents, and their populations, over three analysis periods: 1990 – 2000, 2000 – 2014, and 1990 – 2014. During 2000 – 2014, the most recent period, the median urban extent growth rate for less developed countries cities was 5.7 percent per year compared to 1.1 percent per year in more developed countries cities and 3.1 percent per year in all cities. Average growth rates were higher. A quantity that grows at 5.7 percent per year doubles in size in 12 years and triples in size in 19 years. The median population growth rate over this period in less developed country cities was 3.6 percent per year, compared to 0.7 percent per year in more developed country cities and 2.2 percent per year in all cities. We observed statistically significant declines in the average urban extent growth rate and the average population growth rate from 1990 – 2000 to 2000 – 2014 across all three analysis categories. Despite these declines, the average urban extent growth rate was greater than the average population growth rate at all time periods in each of the categories and this difference was statistically significant. The factors that could explain observed variation in urban extent and expansion were explored in multiple regression models. Population and income were the overwhelmingly dominant factors. These two factors alone explained 85 percent and 65 percent of the variation in urban extent and urban expansion in the 200-city sample. This analysis is very similar to the proposed UN Sustainable Development Goal (SDG) indicator 11.3.1 and offers a first glimpse at globally representative findings. The global sample of cities provides a platform that could be used to monitor progress of other SDG indicators measures as well.