Urban centres shape societies, but there is no systematic global approach analysing how countries are organized around multiple urban centres. We advance understanding by delineating 6,100 city–regions worldwide using a novel framework classifying 30,000 urban centres into four tiers and mapping their nested catchment areas based on travel time accessibility. Our results show extensive interconnectedness among urban centres and with their surrounding areas, with 3.2 billion people having physical access to multiple tiers with 1-hour travel time, rising to 4.7 billion for 3-hours travel time. Importantly, among people living in or near towns and small cities, access to intermediate cities is far greater than to large cities. This highlights the essential role intermediate cities play in engaging surrounding populations. For the first time, city–regions around the world are identified systematically, showing great diversity in how societies are organized across urban tiers, depending on geography and national income. The associated spatial dataset is a powerful tool for regional planning, economic development, and natural resource management.

The Excel files are updated to display the numbers reported in the manuscript by default.