The world's 15 biggest metropolitan areas

"Half of humanity now lives in cities and within two decades, nearly 60 per cent of the world's people will be urban dwellers," according to a UN Habitat study.

As cities expand into mega regions, there is a rapid growth in the population as well. Some of the world's richest cities are also the most populous.

A report by McKinsey Global Institute says that India will have 68 cities by 2030 with a population of over 1 million, 13 cities with more than 4 million people, and 6 megacities with populations of 10 million or more.

Here's a list of the world's 15 biggest metropolitan areas, according to Allianz Knowledge.

1. Tokyo (Japan)

Metropolitan area: 35.2 million people
City: 12.9 million people

Tokyo, capital city of Japan is the most populous metropolitan area and the world's largest metropolitan economy with a GDP of $1.479 trillion at purchasing power parity in 2008.

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2. Seoul (South Korea)

Metropolitan area: 25 million people
City: 10.4 million people

The Seoul National Capital Area is the world's second largest metropolitan area.

Seoul accounts for 21 percent of the country's GDP and is home to major multinational conglomerates such as Samsung, LG and Hyundai.

In 2008, Seoul was named the world's sixth most economically powerful city by Forbes.

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3. Jakarta (Indonesia)

Metropolitan area: 22 million people
City: 9.6 million people

The capital city of Indonesia, Jakarta is listed as a global city in the 2008 Globalisation and World Cities Study Group and Network (GaWC) research.

Jakarta's economy depends on financial services, trade, and manufacturing. In 2009, 13 per cent of the population had a per capita income of over $ 10,000.

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4. Mumbai

Metropolitan area: 21.9 million people
City: 14 million people

Mumbai, the capital of Maharashtra, is the most populous city in India, and the second most populous city in the world.

Mumbai is also the richest city in India and accounts for 6.16 per cent of the country's total GDP. As of 2008, Mumbai's GDP is Rs 919,600 crore ($204.15 billion).

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5. New Delhi

Metropolitan Area: 20.9 million people
City: 9.8 million people

One of the fastest growing cities in the world, the capital city of India focuses on industrial sectors like information technology, telecommunications, hotels, banking, media and tourism. It contributes 4.94 per cent to India's GDP.

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6. Manila (The Philippines)

Metropolitan Area: 20.6 million people
City: 11.2 million people

Manila, the capital of Philippines, is the hub of many scientific and educational institutions.

The city is a major political, commercial, cosmopolitan, cultural, educational and transportation centre of the Philippines.

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7. Sao Paulo, Brazil

Metropolitan area: 20.1 million people
City: 11 million people

One of the richest cities in Brazil, Sao Paulo is also the most important financial centre in Latin America.

Sao Paulo is the 10th richest city in the world and is expected to be the 6th richest in 2025.

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8. Beijing (China)

Metropolitan Area: 19.7 million people
City: 13.3 million people

Beijing is a recognised hub of political, educational, and cultural activities.

Beijing is amongst the most developed cities in China with the tertiary industry accounting for 73.2 per cent of its GDP.
In 2010, Beijing's nominal GDP reached 1.37 trillion RMB.

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9. Shanghai (China)

Metropolitan area: 19.2 million people
City: 13.8 million people

Shanghai represents the booming economy of China. The World Expo organized in 2010, attracted 73 million visitors from around the world.

Shanghai is now aiming to be a global finance hub and international shipping centre.

The city's total GDP grew to 1.687 trillion RMB ($256.3 billion) with GDP per capita of 76,000 RMB ($11,540).

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10. New York City

Metropolitan area: 19 million people
City: 8.3 million people

New York is the most populous city in the United States. A gateway for immigration to the United States, it is also a financial, cultural, transportation, and a manufacturing hub.

New York is the leading centre of banking, finance and communication in the United States.

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11. Mexico City

Metropolitan area: 18.7 million people
City: 8 million people

Mexico City is Mexico's largest city and a political, cultural, educational and financial centre.

Mexico City had a gross domestic product (GDP) of $390 billion in 2008, making it the eighth richest city in the world.

The city was responsible for generating 21 per cent of Mexico's gross domestic product.

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12. Cairo, Egypt

Metropolitan Area: 17.2 million people
City: 7 million people

The economy of Cairo was ranked first in the Middle East region and 43rd globally by Foreign Policy's 2010 Global Cities Index.

Cairo, the capital of Egypt has been the centre the nation's commercial activity.

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13. Kolkata

Metropolitan Area: 15.6 million people
City: 5.1 million people

Kolkata is the commercial capital of eastern India, located on banks of the Hooghly river.

The Kolkata metropolitan area, including suburbs, has a population of over 15 million making it the third most populous metropolitan area in India.

Kolkata served as the capital of India during the British era till 1911.

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14. Los Angeles

Metropolitan area: 14.7 million people
City: 3.8 million people

The entertainment capital, of the world is the most populous city in California and the second most populous in the United States.

Los Angeles has been ranked the third richest city and fifth most powerful and influential city in the world, behind only New York City in the United States.

The Los Angeles combined statistical area (CSA) has a gross metropolitan product (GMP) of $831 billion (as of 2008).

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15. Moscow

Metropolitan area: 13.7 million people
City: 10.5 million people

Moscow is one of largest city economies in Europe and it accounts for 24 per cent of Russia's GDP.

Moscow is the financial centre of Russia and home to the country's largest banks and many large companies.