What makes a place urban?

The quintessence of urbanity is a sustained geographic concentration of strangers. Physical congregation—or corporeal copresence—has wide-ranging environmental and social consequences that produce urban contexts. In practical terms, this means that demographic criteria alone are sufficient to classify a location, settlement, or region as more or less urban. We use a series of thought experiments to demonstrate the conceptual limitations of popular definitions of urbanity, such as the economic structure of a community, the presence of physical infrastructure, the political or administrative status of a geographic unit, or the degree of connectivity between people. We show that these are not essential to what makes a place urban but are instead common epiphenomena associated with places that have a sustained geographic concentration of strangers. This definition does not require a settlement to be permanent, allowing for ephemeral urbanity (dense but temporary settlements), resolving many classic exceptions to previous definitions of urbanity. We suggest that urbanity is best conceptualised and measured on a continuum and discuss how this can be done empirically to advance our theoretical and practical understanding of urban places and urban systems globally.