The World's Ten Biggest Metropolitan Areas

3. Mexico City, Mexico
Metropolitan area: 22 million people
City: 8.7 million people

Mexico City is ten times the size it was in 1940. Now with about 22 million people in the metro area, the Mexican capital generates almost a quarter of the country's wealth. However, with a low population growth of 0.99 percent, the number of people in retirement is expected to rise rapidly in the next decades.

Urban Detail:
Security, air pollution, and traffic congestion are prime concerns in Mexico City – problems that result from poor resource management and unstructured growth. (Photo: Reuters)