Urban Geography: Cities, Megacities, and the World City Hierarchy

The urbanization transition

For most of human history, the vast majority of people lived rural lives on farms. Around 2007, humanity crossed the 50% urban threshold for the first time. Today ~57% of world population lives in urban areas, and the share is growing — especially in developing regions.

Urban form varies with era

• Pre-industrial city — walking-scale, dense, walled, market-and-cathedral center. European old towns (Prague, Toledo, Siena).
• Industrial city — factories along rivers/rail lines, workers' housing nearby, downtown commercial district, streetcar suburbs at edges. 19th-century Chicago, Manchester.
• 20th-century auto-oriented city — highway-connected suburbs, downtown commercial core, malls at edges. Los Angeles, Phoenix, Houston.
• Post-industrial / global city — service and information economy dominant, gentrified downtown, global financial and cultural functions. New York, London, Tokyo, Singapore.

Megacities

Metropolitan area with more than 10 million residents. As of mid-2020s there are 30+ megacities globally, most in Asia and Latin America:

• Tokyo — historically the largest, ~37 million (now slowly declining)
• Delhi — ~33 million and rising fast
• Shanghai, Dhaka, Mumbai, Beijing, Osaka, Karachi
• Cairo, Manila, Buenos Aires, Kolkata, Mexico City, São Paulo
• Lagos, Kinshasa, Istanbul — very fast growth

Only a handful of megacities are in high-income Western countries. Most megacity growth is now in Africa and South Asia.

World city hierarchy

Not all cities are equally influential in the global economy. A world city (or global city) concentrates corporate headquarters, financial services, advanced producer services (law, accounting, consulting), major airports, and cultural production. Rankings by the Globalization and World Cities (GaWC) network typically place New York, London, Tokyo, Paris, Hong Kong, Singapore, Shanghai at the top.

Informal settlements

Where formal urban housing supply falls short of demand, informal settlements — self-built housing on marginal land — expand. Different regions use different names for the same phenomenon: favela (Brazil), township (South Africa), bidonville (French Africa), kampung (Indonesia), villa miseria (Argentina), ashwa'iyat (Egypt). Estimates suggest around a billion people worldwide live in informal settlements.

Primate city / urban primacy

A country's largest city is disproportionately larger than any other. Bangkok, Buenos Aires, Cairo, Lima are canonical examples — each many times larger than the second-largest city in its country. Compare with more balanced urban hierarchies (Germany's Berlin/Munich/Hamburg, Australia's Sydney/Melbourne/Brisbane).

Urban issues

• Housing affordability — worsening in most high-income world cities
• Gentrification — higher-income residents moving into and redeveloping previously lower-income neighborhoods, often displacing existing residents
• Urban heat island — cities measurably warmer than surroundings due to dense hard surfaces, less vegetation, waste heat
• Sprawl — low-density expansion consuming farmland
• Traffic congestion + air pollution — auto-oriented cities
• Water and sanitation gaps — especially in informal settlements of developing-region megacities

Planned cities

Some capitals were planned from scratch to redistribute population or create new political centers: Brasília (Brazil, 1960), Islamabad (Pakistan, 1960s), Abuja (Nigeria, 1991), Naypyidaw (Myanmar, 2005), Astana/Nur-Sultan (Kazakhstan, 1997). Success varies — some attract population, some struggle.

21st-century urban trends

• Smart cities — sensor networks, data analytics, integrated systems
• 15-minute city — Paris-associated planning concept where daily needs are within a 15-minute walk or bike ride
• Transit-oriented development — dense mixed-use around transit stations
• Climate resilience — coastal cities investing in adaptation (New York, Rotterdam, Ho Chi Minh City)