Worldwide Delineation of Multi-Tier City-Regions

Urban centres are pivotal in shaping societies, yet a systematic global analysis of how countries are organized around multiple urban centres is lacking. We enhance understanding by delineating city-regions worldwide, classifying over 30,000 urban centres into four tiers-town, small, intermediate, and large city-based on population size and mapping their catchment areas based on travel time, differentiating between primary and secondary city-regions. Employing a 3-hour travel time cutoff, we identify 1,403 primary city-regions, increasing to 4,210 with a 1-hour cutoff, more indicative of commuting times. Our findings reveal significant interconnectedness among urban centres and with their surrounding areas, with 3.2 billion people having physical access to multiple tiers within an hour, and 4.7 billion within three hours. Notably, among people living in or closest to towns or small cities, twice as many have easier access to intermediate than to large cities, underscoring intermediate cities' crucial role in connecting surrounding populations. This systematic identification of city-regions globally, uncovers diverse organisational patterns across urban tiers, influenced by geography, level of development and infrastructure, offering a valuable spatial dataset for regional planning, economic development, and resource management.