Right next door, to the north, sits the even larger settlement of Nezahualcoyotl, where more than three million people live in similar conditions, forming what has been described as the world's biggest slum.

The next day, politically active people from Bombay's biggest slum gathered across town in a grimy clinic to push for sewage lines and the removal of rotting garbage from their neighborhood.

Magnificent high-rises tower above some of the world's biggest slums.

Brazilian security forces occupied one of the biggest slums in Rio on Sunday.

"America is the one rich country with the biggest slums, the least democratic and least developed health system and the most niggardly attitude against its old people."

But a major obstacle remains: how to attract new customers to a borough that is seen by many outsiders as one big impoverished, crime-ridden slum.

In part, those chasms reflect the difficulty of getting teachers to work in remote rural areas and big urban slums.

In Kaduna the two biggest slums, Rigasa and Narahi, suffered the greatest devastation during the upheaval last month.

As one ventures deeper into the neighborhood, the environment degrades into one of Kampala's biggest slum.

Therefore, most of the population, not only in the big slums in the exploding mega-cities of the south, but also in the emerging middle class, does not have even near-normal sanitation.