Definitions of 'urban' have become more nuanced since the AR5 review with the publication of the OECD report 'A new perspective on urbanisation' . This report presents two new global definitions of urbanisation reflecting the degree of urbanisation on a continuum of cities, towns and semi-dense areas, and rural areas. The OECD estimates almost half the world's population  live in cities, while just 24% live in rural areas and 28% live in towns and semi-dense areas . In addition, the OECD report defines metropolitan areas as functional urban areas together with their surrounding commuting zones 'to capture the full extent' of a city's working population. Metropolitan areas account for 54% of total world population, with the OECD estimating that commuting zones representing 17% of the overall metropolitan population, rising to 31% in high-income countries. In the context of these global definitions, this chapter identifies 'cities and settlements' as concentrated human habitation centres    that are fundamentally inter-connected to other urban centres and rural areas as nodes within broader networks.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report