Where the sidewalks end.

• Author: Sheehan, Molly O'Meara

One out of every seven people now lives in a slum--or at least that's the UN's best estimate. More and more slum residents are organizing to improve their lot, as their numbers swell in cities all over the world.

SOUINTING IN THE SUNLIGHT, George Ng'ang'a leads me up a mound of dirt and rubbish on the edge of his Nairobi neighborhood to take in the view. To the south unfolds a safari scene of grassy plains dotted with acacia bushes as far as I can see. To the north stands a dense gathering of gangly shacks cobbled together with cloth, mud, tin, rocks, and sheets of plastic. There are about 800 homes in all crowded onto some 5 to 6 hectares, says Ng'ang'a.

On city maps, the location of this settlement--called "Mtumba" by the 6,000 people who live there--shows up as prime habitat for rhino and giraffe. That's because this unsanctioned community lies on the edge of Nairobi National Park. Mtumba is only one of the many slums around Nairobi. In fact, more than half of the residents of Kenya's capital city cannot afford to live in "formal" housing, and have been forced to find shelter in slums like this one.

Ng'ang'a turns to me and tells me to call him "Castro," which, he says, is his nickname. He has the physique of a bear and is clean shaven, but he insists he was thin and bearded in his youth. I'm not sure if he's joking about the physical resemblance, but it' s clear that he's passionate and politically active. For several years in a row the people of Mtumba have chosen Castro to be the leader of the community's governing council in informal elections-informal because the city government does not serve slums, so the people of Mtumba have found their own ways to organize and police themselves.

"We can't depend on the government for anything," says Castro as we walk through the settlement. One of his neighbors, a solemn man named Tom Werunga, joins in our stroll. Werunga, who carries a Bible, tells me that he's a pastor. He points out a water tap--one of two small spigots that supply water for the entire settlement. But no city water is piped here. Instead, these taps are fed by private companies that truck in tanks. And they sell their water at a premium. As of yet, no company has seen fit to establish any sort of business setting up toilets or sewers. Instead the 6,000 people who live here share three flimsy pit latrines. "Flying toilets," I learn, are of human excrement that are flung atop roofs or into rubbish piles.

I am scribbling notes, trying to pay attention to the latrines Castro is showing me, but my eyes are stinging in the acrid air. Cinders and fumes from untended piles of burning trash mingle with ash and smoke from charcoal cooking fires where women prepare meals. At night, kerosene fumes from lanterns join the stew. More than 80 percent of Nairobi's households use charcoal for cooking, but the air is worst in neighborhoods such as this, which lack both electricity and trash removal.

Everything in Mtumba, it seems, is insecure and informal. There is no land ownership. There is no public infrastructure. And there is no protection provided by the law. Mtumba's families have moved together twice before, says Castro. They landed in this location in 1992. Since then Nairobi officials have threatened to evict the community several times. And on one occasion, he says, officials sent in bulldozers to completely demolish the settlement. Some families have seen their homes destroyed as many as 10 times. "Every day we are waiting for the demolition squad," says Castro. "We are refugees in our own country."

IT IS NEIGHBORHOODS LIKE MTUMBA -- Greenwich Village in Manhattan or the Rive Gauche in Paris--that are setting the trends for modern urban living. The UN estimates that somewhere between 835 million and 2 billion people now live in some type of slum, whether in a kampung in Indonesia, a favela in Brazil, a gecekondu in Turkey, or a katchi abadi in Pakistan. The population of slum dwellers in some of the world's largest cities--Bombay, Bogota, and Cairo, for example--now outnumbers the population of people living in formal housing.

In many cities--particularly in sub-Saharan Africa and South Asia--explosive urban growth is combining with the world's worst poverty to fuel the proliferation of slums. The world's population increased by 2.4 billion in the past 30 years, and half of that growth was in cities. Over the next three decades, global population is expected to increase by another 2 billion. Demographers expect that nearly all of that population increase will end up in developing-country cities, due to urban migration and high birth rates (see graph, page 23).

While most poor people still live in rural areas, poverty is rapidly urbanizing. As of 1998, more than 1.2 billion people were living in extreme poverty (on less than the equivalent of about $1 a day), unable to meet even basic food needs. Martin Ravallion of the World Bank estimates that the urban share of the world's extreme poverty is currently 25 percent. He projects that it is likely to reach 50 percent by 2035.

A number of factors are driving the growth of cities worldwide. Rural economies in many regions have been hard hit by environmental degradation, military or ethnic conflicts, and the mechanization of agriculture, which has curbed the number of rural jobs. The prospect of better-paying jobs has drawn many people to cities.

Latin America is by far the most urbanized region of the developing world. About 75 percent of people in Latin America live in cities--along with 75 percent of the poor. While only 37 and 38 percent of Asians and Africans live in cities respectively, a number of nations in these regions are beginning to see poverty shift to urban centers. For instance, the proportion of people living below the poverty line in rural Kenya between 1992 and 1996 increased from 48 to 53 percent, while the share of people living below the poverty line in Nairobi doubled from 25 to 50 percent.

Castro tells me that his family's land was taken by the colonial Kenyan government in 1952 to build a golf course. "My father was a businessman," he says, "so we went to different places, like nomads." Castro continued the itinerant lifestyle as a young man, but then he got married and began looking for a better life for his family. Eventually, he says, "we came to the Nairobi slums, even though I have an education."

IN GENERAL, THE "OFF-THE-BOOKS" OF MTUMBA and other informal communities confers certain advantages. Rents are lower than in formal housing. There are no property taxes. Residents can skirt cumbersome zoning laws that separate housing from businesses, and set up shop inside their homes or just outside. Mtumba's commercial strip boasts rows of brightly painted storefronts, each about 1 meter wide. There are produce stands, coffee shops, a "movie house" showing videos, a barber shop, and an outfit that collects old newspapers. But the short-term benefits of living and working outside the formal economy rarely outweigh the long-term costs to residents--and to the cities that have failed to address their needs.

Slums are often located in a city's least-desirable locations--situated on steep hillsides, in floodplains, or downstream from industrial polluters--leaving residents vulnerable to disease and natural disasters. Another long-term cost is the premium residents pay for basic services. The African Population and Health Research Center recently released a report showing that Nalrobi's slum dwellers pay more than residents of wealthy housing estates for water--and, as a result, use less than is adequate to meet health needs. "A family needs 100 liters per day for drinking and cleaning," says Mtumba's Tom Werunga. As that much water costs 25 Kenyan shillings (30 cents), it could easily eat up half the income of people who, on average, make about 50 to 60 shillings (60 to 75 cents) per day.

Landlords operating in slums can easily gouge their tenants without fear of legal...