megacity

A megacity is a metropolitan area with at least 10 million inhabitants, typically defined by the size of the urban agglomeration rather than administrative boundaries. The term emerged in urban planning and demographic research in the mid-20th century and is used by international organizations to describe very large urban concentrations. Because definitions vary, some sources measure population within city limits, while others use the broader urbanized area.

Megacities typically concentrate economic activity, services, and cultural life, but they also place heavy demands on housing, transportation, water, energy, and waste management. Infrastructure often struggles to keep pace with rapid growth, and informal settlements may be prevalent in parts of the city. Environmental issues, air and water quality, flood risk, and climate vulnerability are common concerns, as are governance fragmentation and social inequality.

Asia hosts the majority of megacities, with several exceeding 20 million residents. Other regions in Africa, Latin America, and Europe also contain megacities, though fewer in number. Estimates vary by methodology; the United Nations counted about 33 megacities in 2018, with the count rising as urbanization continues.

Urban planning and policy responses focus on regional governance, mass transit systems, affordable housing, and climate adaptation. Effective megacities often pursue integrated planning, inclusive governance, and data-driven management to balance economic opportunity with livability and resilience in the face of rapid population growth.