More than half the world's population already lives in cities and the urban population of sub-Saharan Africa is projected to double by 2030.

BBC: Africa: Feeding the rising urban population

According to a study by the Department of Housing and Urban Development, sub-prime loans are five times as common in black neighbourhoods as in white ones.

ECONOMIST: Lawmakers, state and federal, are mounting an attack

Habitat, 62% of the urban population in Sub-Saharan Africa lives in slums, which it describes as being typically characterized by deplorable living conditions, a feeling of insecurity and inadequate infrastructure for basic energy, sanitation and water services.

CNN: High-tech shack brings solar power to slums

According to the Gates Foundation website, the focus of the family planning initiative will be on urban areas in sub-Saharan Africa and South Asia, areas where maternal and infant mortality rates are high and contraception use is low.

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"If 33% of (the) urban population lives in slums -- they may live in sub-human conditions, but still, they are a drain on the economy, " he said.

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According to the World Health Organisation, dengue is now endemic in more than 100 tropical and sub-tropical countries around the world, affecting some 50m people a year, mostly in urban or semi-urban areas.

ECONOMIST: Dengue fever

But it also looks at three sub-watersheds, said Lucas, one that is relatively pristine, one rapidly urbanizing, and one already very urban.

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