A global analysis of multifaceted urbanization patterns using Earth Observation data from 1975 to 2015

Urbanization as a global phenomenon is a multifaceted process. Here we do the first global attempt to characterize the complexity of urbanization from 1975 to 2015 in terms of population, built-up structure, and greenness per 5 × 5 km2 grid covering global inhabited areas, using Earth Observation data sources. Our results emphasize the multifaceted nature of urbanization that varies greatly across regions and times, in addition to the steady expansion of built-up land. Increased population density and built-up patch density were the dominant characteristics in Asia and Africa, while urbanization in Europe and North America took a rather steady pace, combined with widespread greening. According to the urbanization types identified by a self-organizing map (SOM) algorithm, a large proportion of urban and suburban areas experienced two dynamic urbanization types – built-up extension/leapfrog and built-up infill with large population increase. During different historical periods (1975–1990, 1990–2000, and 2000–2015), annual rates of increase in population and built-up density were slowing coinciding with an increasing greenness – signaling that urbanization processes are becoming less intense, more compact, and ‘greener’ over the most recent period. Our findings facilitate the comprehensive understanding of global urbanization that is a complex process with many local variations and characteristics, and underscore the need for region-based strategies towards sustainable development instead of a ‘one-size-fits-all’ policy for cities.