Megacities

Megacities are giant cities. The term has been in common use since the 1980s to characterize metropolitan areas with very large total populations. Most commonly, specialists and UN demographers use the term in comparative urban studies, referring to metropolitan areas with more than 8 or 10 million inhabitants. The underlying argument is that the population size of these metropolitan areas gives them special characteristics. Attention typically focuses on the total population of the metropolitan area--usually a major city and its surrounding suburbs.

Metropolitan areas, also known as urban agglomerations, are notoriously difficult to define because administrative definitions vary from country to country and because the cities integrate in many different ways with their surrounding regions. In less developed countries, the rural poor may seek work in the cities as migrant laborers, and villages become integrated with metropolitan labor markets.

On the urban fringe, agriculture, factory farming, and industries like brickmaking intensify to meet metropolitan demand, while commercial strips often line the intercity highways. In more developed countries, towns and villages around the metropolis may evolve into satellite, bedroom, second-home, and recreational communities, while suburbs may sprawl outward at lower and lower densities. Commuters and suburbanites may seek to enjoy rural landscapes and simulate rural lifestyles yet gain their livelihoods in the metropolitan economy. Planners may seek to preserve rural and wilderness areas as greenbelts and parks, but urban development often simply leapfrogs the preserved areas, creating new metropolitan satellites.

As world population rises and urbanization continues, the proportion of the world's megacities located in less developed countries increases, and the threshold size for megacity definition tends to rise. In 1950, only one metropolitan area in the world, New York, had more than 10 million inhabitants. By 2005, however, the number had risen to 19 metropolitan areas, all but four of them in less developed countries. Two alternative terms, metacities and hypercities, have now emerged to embrace metropolitan areas with more than 20 million inhabitants. Tokyo is the first metacity, but all the others most likely to cross this threshold by 2015--Dhaka, Mumbai, Sao Paulo, Delhi, Mexico City, and Shanghai--are in developing countries.

Characterizing all giant metropolitan areas are high levels of congestion, pollution, land values, and living costs in relation to neighboring less densely populated regions. Both in rich and poor countries, however, megacities usually have higher average incomes and productivity levels than smaller cities and rural areas, and they are tremendously important foci of business activity. Anti-urbanists emphasize their problems, pro-urbanists emphasize their dynamism and synergies, and comparative researchers tend to emphasize the development characteristics of the countries within which the megacities are located. Some megacities--most notably Tokyo, New York, and London--are dynamic "world cities" playing pivotal roles in the global system. At the other extreme, descriptions of megacities like Kolkata, Karachi, Lagos, and Kinshasa tend to emphasize mass poverty and diseconomies of urban size.