Global mapping of urban-rural catchment areas reveals unequal access to services.

Using travel time to cities of different sizes, we map populations across an urban-rural continuum to improve on the standard dichotomous representations of urban-rural interactions. We extend existing approaches by 1) building on central place theory to capture the urban hierarchy in access to services and employment opportunities provided by urban centers of different sizes, 2) defining urban-rural catchment areas (URCAs) expressing the interconnection between urban centers and their surrounding rural areas, and 3) adopting a global gridded approach comparable across countries. We find that one-fourth of the global population lives in periurban areas of intermediate and smaller cities and towns, which challenges the centrality of large cities in development. In low-income countries, 64% of the population lives either in small cities and towns or within their catchment areas, which has major implications for access to services and employment opportunities. Intermediate and small cities appear to provide catchment areas for proportionately more people gravitating around them than larger cities. This could indicate that, for countries transitioning to middle income, policies and investments strengthening economic linkages between urban centers and their surrounding rural areas may be as important as investing in urbanization or the rural hinterlands. The dataset provided can support national economic planning and territorial development strategies by enabling policy makers to focus more in depth on urban-rural interactions.