UNITED NATIONS.- Mexico City has for years been the third most populous city in the world, but a new demographic study published by the United Nations has now ranked it as the fourth most populous.

Entitled "World Perspectives of Urbanization" the report doesn't just rank the most populous and least populous cities, but also cites possible risks that large increases in population may bring about as well as possible solutions.

For 2030, it is projected that the world will have forty-one mega cities with 10 million or more residents.

The most populous city in the world in 2014 is Tokio, Japan coming in at 37.8 million inhabitants, followed by Delhi, India with 24.9 million; Shanghai, China with 22.9 million; Mexico City is followed closely by Sao Paolo, Brazil with 20.8 million inhabitants.

New York in the nineties was the third most populous city, but has now been bumped down to ninth position, followed by Cairo, Egypt. Mexico City is expected to move down to tenth place by 2030 due to a slower demographic growth compared to other countries with higher growth.

Mexico is a highly urban country that is expected to have eighty percent of its population residing in cities by 2020, a symptom of a world tendency among other cities with medium-high incomes, such as Brazil, China, and Iran. In 1950, only twenty percent of the population of these countries lived in urban areas, but this has increased to sixty-three percent in 2014 on average. But now, these countries have the most urban growth or expected urban growth as highly developed countries exceed eighty or ninety percent of their population in cities, and basically cannot grow any more.

Other important facts in the report include:

More than half of the seven billion people in the world live in urban areas.

The primary reasons that cities in Asia and Europe have decreased in population or are not increasing is because of economic problems, low fertility rates, and natural disasters along with emigration.

When confronted with migration of the world population to megapolises or mega-cities, the UN recommends that countries implement policies that ensure the benefits of urban growth take place in an equative and sustainable manner.

The main challenge for urbanized cities will be to provide basic services such as health, education, housing, infrastructure, transportation, energy and employment.

As far as rural population goes, this will continue to grow to reach 3.4 million in 2020 at which point it will decrease, and is expected to decrease to 3.1 million by 2050.

Africa and Asia are urbanizing at a higher rate than other regions in the world.

Of the 28 mega-cities, sixteen are located in Asia, four in Latin America, three in Africa, three in Europe, and two in North America.

Via Voice of America and AnimalPolitico.com

Jose.Sanchez@sandiegored.com

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