In Kathryn Neckerman's world, there are five banks within a five-minute walk of her Manhattan apartment and a staggering variety of goods and retail shops.

The problem is not everyone lives in her world, said Dr. Neckerman, a Columbia University sociologist whose interests include studying "built environment," inequality and urban policy.

Dr. Neckerman spoke at the University of Pittsburgh's Center for Race and Social Problems yesterday on how spatial accessibility -- proximity to basic retail and services -- varies across New York City neighborhoods.

She is co-investigator of a National Institutes of Health project on built environment, the impact of land use, public transit and housing on physical activity, diet, obesity and other aspects of health.

The results of the research are new and show that in many urban areas, some poor and black communities are so bereft of services and retail that residents are forced to pay what she called a "time tax," either extra money or loss of personal time, to access basic services.

In some communities, said Dr. Neckerman, residents must take a cab to get to the bank, rely on costly check-cashing agencies and take two buses to get to the supermarket.

This reality hammers at low-income families, especially those with limited access to services or reduced mobility.

On average, Dr. Neckerman said, low-income families earn $15,000 a year and because of spatial inequality large chunks of it are gobbled up by spending up to $2,000 a year on the check-cashing service, or by using a car, which can cost $3,500 a year.

"Time is money," said Dr. Neckerman, and all the time and costs put pressure on families.

That's in addition to new welfare requirements, which mandate job-training and rob families of time to go back to school, take care of their health or read to their children.

"We need to think about the time tax," she said.

Inner-city neighborhoods, those that are predominantly African-American and withered by fleeing industries and an out-migration of the middle class, are hit the hardest by the tax. But so are middle class black neighborhoods on the fringes of the central city, said Dr. Neckerman. They are impacted not so much by poverty, but by racism and discriminatory practices, which can limit subway stops and access to transportation, and fuel perceptions of communities as being unsafe.

Black neighborhoods fare the worst, she said. Neighborhoods with a high density of immigrants fare better, as they are more likely to have higher rates of self-employment and perhaps greater access to bank loans, which historically have been limited for blacks because of racism.

She cautioned that the research must be examined more deeply. One of the first problems, she said, could be that it treats all retail establishments of equal value. They are not. A check-cashing office is not a bank; a fast-food establishment is not a full dining restaurant and a corner bodega is not a full-service drug store or grocery.

Future developments could be further shaped by the trend to break up inner city areas of concentrated poverty, such as housing projects.

Also, as the push toward gentrification brings higher-income white residents closer to a city's core and its cultural amenities and employment, it's possible there could be further displacement of the poor. It's a trend that could be exacerbated as businesses like Starbucks begin to identify neighborhoods for new sites, which help accelerate gentrification.

These issues, Dr. Neckerman said, are important aspects of conversations between urban planners and public policy officials on environmental issues, traffic congestion and health consequences.

Those conversations must take place, she said. Otherwise, "displacing the poor and minorities intensifies the trade-off they have to make between time and money."