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What do 7 billion people look like?

Paulo Santos / Reuters

Roman Catholic pilgrims press together while following the image of the local saint, Our Lady of Nazareth, as it is paraded Oct. 11, 2009, during the annual Cirio de Nazare procession, the country's biggest religious festival, in Belem, at the mouth of the Amazon River. More than 1 million Catholics, many from communities along the Amazon River's tributaries, converged on Our Lady of Nazareth basilica to participate in the event.

Reuters

People crowd in a swimming pool to escape a summer heat wave July 4, 2010, in Suining, China.

As the world population explodes, so does the growth of cities, especially in Asia and Africa.

Globally, one in two people lives in an urban area, a milestone reached in 2007, says the United Nations Population Fund, the agency that predicts world population will reach 7 billion on Oct. 31.

In about 35 years, two out of three people will live in cities and towns, the agency predicts.

Nicky Loh / Reuters

Motorists crowd at a junction during rush hour in Taipei on Oct. 29, 2009. There are around 8.8 million motorcycles and 4.8 million cars on Taiwan's roads. Nearly all motor vehicles and inhabitants are squeezed into a third of the island's area, resulting in high concentrations of polluting emissions in the places where people live and work, according to official reports.

Morris Macmatzen / Reuters

Sunbathers and roofed wicker beach chairs line up along the beach on the bay of Travemuende, a popular holiday resort at the Baltic sea near the northern German city of Luebeck, on Aug. 5, 2007.

The fastest growth is seen in sub-Saharan Africa, which has the world's highest birthrates and deepest poverty. The regional population of nearly 900 million could reach 2 billion in 40 years.

"Most of that growth will be in Africa's cities, and in those cities it will almost all be in slums where living conditions are horrible," said John Bongaarts of the Population Council, a New York-based research organization.

Akintunde Akinleye / Reuters

A man walks on a pedestrian bridge overlooking traffic in Lagos, Nigeria, on Sept. 18, 2006.

Nigeria’s commercial capital, Lagos, with an estimated 15 million people and a 6 percent growth rate, is expected to overtake Cairo soon as Africa's largest city. Problems with traffic congestion, sanitation and water supplies are staggering; a recent article in UN-Habitat said two-thirds of the residents live in poverty.

India is Asia’s second-largest country with 1.2 billion people, but by 2030 it may surpass No. 1 China, now with 1.34 billion people.

Reuters

A view of a residential building in Shanghai on March 18, 2009.

Reuters

Job-seekers crowd a job fair in Wuhan, China, on March 17, 2007. Unemployment could be long-term trouble for China, with the number of jobless urban residents alone exceeding 15 million, the China Information News quoted a senior official as saying, Xinhua News Agency reported.

Across India, teeming slums, congested streets, and crowded trains and trams are testimony to the country's burgeoning population.

At 6 p.m. on a typical evening in Mumbai, India's financial hub, 7 million commuters swarm out of their offices and head to railway stations for rides home on an overtaxed suburban rail network. Every few minutes, as a train enters the station, the crowd surges forward.

Every ride is a scramble. Each car is jam-packed; sometimes, riders die when they lose their foothold while clinging to the doors.

- msnbc.com editors Natalia Jimenez and Jim Gold, with wire service reports.

For more information: Beijing's 'hubs' haven't curbed population pressures

See more images and posts related to the seven billion population milestone

K.K. Arora / Reuters

Hindu devotees travel on a crowded passenger train to take part in the "Guru Purnima" festival near Mathura, India on July 24, 2010.