Fragmented by Nature: Metropolitan Geography, Urban Connectivity, and Environmental Outcomes

Abstract

Physical geography has long been identified as critical for urban development, land use, and environmental outcomes in cities worldwide. However, the literature has yet to provide comprehensive, quantitative analyses of the global extent and impact of urban geographic barriers. Our study introduces three novel indexes: the share of natural barriers, non-convexity (a measure of natural fragmentation), and the average road detour, to measure and study the practical reach and effects of natural barriers around global cities. We calculate these indexes for areas in and around four separate global city-boundary definitions, augmenting the original data with relevant additional variables. We find that natural barriers lead to more complex transportation environments and are associated with higher urban densities, smaller urbanized footprints, taller buildings, and less pollution, but also with lower incomes and smaller populations. To draw meaningful policy conclusions, comparative research about environmental, economic, and social outcomes across global cities should always account for their surrounding geographies.

Keywords: Urban natural barriers, complex road morphology, sustainable urban development, metropolitan growth