NYCMap is pronounced "nice map," according to city officials, who have spent $20 million of the taxpayers' money so far on this computerized mapping project. But, though the public paid for it, this really cool map is largely unavailable to the public. Some people think that is not very nice.

Maps are probably older than written language, the first maps dating back at least 5,500 years ago. Maps changed radically some five centuries ago at the onset of the age of exploration, changed again with aerial photography and again with space flight. Over the last 20 years, there has been another revolution in mapping technology, which has changed the way large cities function.

In any large city, every city agency, whether sanitation, or transportation or health, produces whole libraries of maps; how can construction crews lay new wires if they don't know what's there already? Too often, though, the maps used in different corners of the city government haven't quite corresponded with one another, resulting in…municipal chaos.

The new computer-generated "geographic information systems" reside in powerful databases that can hold a unified picture of all of the different layers of geography and infrastructure that make up a major city. That includes everything from bedrock and bodies of water, to gas mains and sewer tunnels, to tax lots and bus routes.

NYCMap is just such a system, one of the most sophisticated in the world. And therein lies the dilemma: How dangerous is it to let the public see the world-class map its tax dollars made possible? Access to NYCMap is tightly regulated, for fear the detailed urban plan could aid a terrorist attack.

Critics think this is wrong.

"Access to NYCMap should be free," said Gary Ostroff, vice president of Community Cartography, at a recent hearing of the City Council's Technology in Government Committee. "We live in a democracy. The government has no business collecting information it doesn't need, and if it does collect it, the information must be made public. … There should not be a monopoly on the holding of that data."

Work on NYCMap began in 1996, using a method of precise aerial photography which places geographic features like pavement edges and building footprints within two feet of their real position. About 7,500 photos were digitally dissected to produce a computerized "base map" of all five boroughs that charts everything from streets and buildings to subway entrances and manhole covers. The first version of NYCMap was completed in 1999. By 2004 the city had spent about $20 million on the project.

NYCMap provides a foundation for plotting and analyzing almost any kind information about the city: census data, demographic trends, crime statistics, school performance, voting patterns, etc. Map users can turn layers of information on or off as needed. For instance, a police department planner might want a neighborhood map that shows precinct lines, hospitals, schools, and crime statistics. A health official worried about West Nile virus in the same neighborhood might hide the precinct lines and crime stats, and show bodies of water instead.

City agencies and approved contractors can access the core NYCMap database to build their own applications on top of it. According to Marsha Kaunitz, director of Citywide GIS at the Department of Information Technology and Telecommunications, city agencies have created custom applications as diverse as mapping crime statistics, managing construction activities, dispatching emergency responders, and tracking sanitation trucks.

However, average New Yorkers have no direct access to the high-tech map they paid for. The city maintains two public Web sites built on NYCMap: the New York City Map Portal, and a site called My Neighborhood Statistics. Both sites will map an address and display some public information about the area. But neither service lets citizens see the detailed aerial photographs that NYCMap contains.

Most important, private citizens are prohibited from downloading the raw data that would let them invent new uses for NYCMap. A small real-estate broker might want to analyze the data to decide which neighborhoods to invest in, for instance. A senior citizens center might need it to design a program that shows their members the best way to get to public facilities near their homes, taking into account the special transportation needs of the elderly. An academic might hope to study gentrification patterns. Under current rules, none of them have access unless they become licensed as approved vendors to the city.

At the City Council hearing, mapping experts and community advocates agreed that the general public should not be able to see maps of sensitive infrastructure, such as gas mains and the electrical grid. But they said much of the information being held back by the city is not dangerous, and is already available in other public databases or visible to any pedestrian on the street.

"There is a burden to make the case" for restricting each layer of NYCMap, said Alan Leidner, a former director of Citywide GIS, who has been called the father of the city's mapping efforts. "There has got to be a specific reason why that particular layer is considered dangerous and another is not." He also pointed out that the licensing system gives incumbent contractors with access to NYCMap a strong advantage over challengers in designing bids for new work from the city.

Other cities around the world let the public have the kind of information New York City holds back. Residents of both Boston and Philadelphia, in fact, can see detailed aerial photos of their neighborhoods and download the raw data to build their own maps. The State of New York also lets the public download raw map data -- for any county outside of New York City, that is.

"We understand that other cities such as Boston and Philadelphia enjoy less restrictive policies than ours," Marsha Kaunitz testified at the council hearing. "However it is important to note that New York City is unique, both in the specificity of the data contained within our base map and in the level of risk we operate under."

Councilmember Gale Brewer, chair of the Technology in Government Committee, asked Kaunitz to publish a clear policy for what data is available and how interested parties can petition to use it. Later, she promised to keep pursuing the issue of widening access to NYCMap. "We will not let this go away," she said.