PARKING spaces on the Upper West Side are precious resources, to be hoarded like coal in wartime. The familiar street-cleaning shuffle requires paramilitary levels of vigilance and guile. So it is no surprise that the city is eyeing the neighborhood as a place to test a new program that would raise and lower the price of parking to match demand.

The system, known as performance-based pricing, was pioneered by Donald Shoup, a professor of urban planning at University of California, Los Angeles. Under the system, which is in use in Pasadena, Calif. and part of Washington, D.C., the price of parking fluctuates over the course of the day.

In peak periods, like the early evening, prices are kept high enough to dissuade some drivers from parking, with the goal of having two spots per block unoccupied at any time. Advocates of the system say it eases congestion and lowers emissions by sparing drivers the usual "cruise" in search of parking.

Over the last year, officials of the Columbus Avenue Business Improvement District have told the city they are willing to try out the new system, in return for street improvements like bike racks, benches, curb extensions and bike lanes. The city never formally agreed to such an arrangement, but Barbara Adler, executive director of the business district, said she learned a few weeks ago that performance-based pricing might be in the works for the avenue.

MICHAEL CRONIN's job as a college admissions officer took him to India two or three times a year, so he had already seen the usual sites - temples, monuments, markets - when one day he happened across a flier advertising "slum tours."

"It just resonated with me immediately," said Mr. Cronin, who was staying at a posh Taj Hotel in Mumbai where, he noted, a bottle of Champagne cost the equivalent of two years' salary for many Indians. "But I didn't know what to expect."

Soon, Mr. Cronin, 41, found himself skirting open sewers and ducking to avoid exposed electrical wires as he toured the sprawling Dharavi slum, home to more than a million. He joined a cricket game and saw the small-scale industry, from embroidery to tannery, that quietly thrives in the slum. "Nothing is considered garbage there," he said. "Everything is used again."

Mr. Cronin was briefly shaken when a man, "obviously drunk," rifled through his pockets, but the two-and-a-half-hour tour changed his image of India. "Everybody in the slum wants to work, and everybody wants to make themselves better," he said.

Slum tourism, or "poorism," as some call it, is catching on. From the favelas of Rio de Janeiro to the townships of Johannesburg to the garbage dumps of Mexico, tourists are forsaking, at least for a while, beaches and museums for crowded, dirty - and in many ways surprising - slums. When a British man named Chris Way founded Reality Tours and Travel in Mumbai two years ago, he could barely muster enough customers for one tour a day. Now, he's running two or three a day and recently expanded to rural areas.