The City Expansion Indices were created by the World Resources Institute with data from Yale's School of Forestry and Environmental Studies (Yale F&ES), the European Comission's Joint Research Centre (EC JRC) and the National Aeronautics and Space Administration (NASA). The data portray outward growth, upward growth, and the ratio of the upward to outward growth of built form in 499 cities around the world over the years 2000-2014. The form of growth has important repercussions for energy consumption, travel distances, differences in access to services between the city's core and peripheral areas, costs of service provision (water, sanitation, transportation, electricity), size of labor markets, productivity and agglomeration benefits. Urban built form and growth trends also have implications for potential climate-related risks and vulnerabilities.
To create this analysis, two remotely sensed data sets were combined - mean summer backscatter power ratio (PR) from NASA's SeaWinds microwave scatterometer (Ku-band, 13.4 GHz) and built-up area from the multitemporal Global Human Settlement Layer (GHSL). Both data sets were reprocessed to have an equivalent spatial resolution to match the coarsest data set (0.05°). The data shows outward growth of urban built-up area between 2000 and 2014 measured from the Global Human Settlement Layer (GHSL) and upward growth between 2001 and 2009 measured using the power ratio (PR) from NASA’s SeaWinds microwave scatterometer.
For all cities with metropolitan populations greater than 1 million people, LandScan data created by the Oak Ridge National Laboratory comprised 499 cities. This large sample size captures the most significant urban areas around the world. The latitude and longitude of each urban center identified by LandScan were used. Then a grid of 11x11 pixels was used, which comprised 121 pixels per city, to do the analysis. This grid essentially acts as a cookie cutter for the analysis and is irrespective of the administrative boundaries. In other research by Frolking et al. (2013) and in this preliminary analysis, an 11x11 grid was determined sufficient to capture most of the urban areas for most cities. However, for some exceptionally large cities, this cookie cutter may not include the entire administrative boundary of the city. Likewise, for smaller cities, the grid may include neighboring towns. Although cities vary in size, the rationale behind using this cookie cutter is to provide a consistent and uniform analysis across the cities.
This analysis centered on first extracting these 11x11 grids for each city with a population greater than 1 million people, identified using the dataset Populated Places from Natural Earth. Then cells that had an urban built-up value of less than 20 percent in 2014 were in the GHSL data were masked out. To compare urban expansion around the world urban pixels were aggregated to get a value for outward and upward growth per city.
Upward and Outward Expansion Index
When averaging values to identify growth across a city, the variation within the city is lost therefore it is agnostic to a city's administrative boundaries. From the analysis, it was found that the sum statistic is the most appropriate for creating an index to measure and compare levels of outward and upward growth across cities. Upward growth data is from 2001-2009, outward growth data is from 2000-2014.
Mahendra, A. and K.C. Seto, 2019. "Upward and Outward Growth: Managing Urban Expansion for More Equitable Cities in the Global South." Working Paper. Washington, DC: World Resources Institute. Available online at www.citiesforall.org. Accessed through Resource Watch, (date). www.resourcewatch.org.
2000 - 2014