Population:
According to 2009 estimates, Mexico is home to eleven cities housing a million or more people. Of these eleven cities, Mexico City is the largest in terms of population. Over 20 million people live in the Mexico City area, though the city has only achieved megacity status fairly recently.
Source:
Mexico's Population
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This website shows the decreasing percentage of urban population of Mexico City in comparison to other urban areas:
Migrants Between Federal Entities, Mexico 1900
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