This map shows the world's 20 most populous urban areas in 2004. With 21,503,000 people, Mexico City ranks third.
Click on image for full size
Data courtesy of the World Gazetteer; illustration courtesy of Mike Shibao, UCAR.


Mexico City, where the field campaign MILAGRO takes place, is a "megacity." A megacity is defined as having 10 million or more inhabitants.

The 21st century is definitely shaping up to be the Urban Century. For the first time in human history, more people live in urban areas than do not. (An "urban" area is a city; the opposite is a "rural" area, which means in the countryside.) In 2000, the world supported 411 cities that each had more than one million inhabitants. While the majority of the world's urban population used to live in Europe and North America, today the biggest growth is happening in developing nations, especially in Asia.

People are moving from the countryside into cities in search of more economic opportunities. That is, they expect to make a better living while working in the city. During the last decade, for example, an estimated 150 million rural Chinese moved to the nation's urban areas, filling megacities like Shanghai and Beijing.

In the future, more and more megacities will form. It is estimated that the number of megacities will reach 26 by 2015. Most cities lack the services to support so many new people coming into them, resulting in unsustainable growth and the pollution that so often accompanies it.

Last modified February 14, 2006 by Nicole Gordon.

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