A DECADE AGO, in his celebrated book Mirror Worlds, Yale computer-science professor David Gelertner envisioned what he called a "universe in a shoebox": all the key statistics about any urban settlement could (and would, Gelertner argued) one day be stored in a single computer program -- a "mirror world" that would help us govern and navigate the real world better.

For most of the past decade, Gelertner's vision has remained tantalizingly theoretical. But two ambitious new mapping projects in America's two largest cities are attempting to make the mirror world a reality. New York City and Los Angeles, already seen as the epicenters of American narcissism, are getting to know themselves a lot better these days. With sophisticated computer simulation and mapping projects underway, they'll soon know themselves down to the square foot. Both maps will integrate aerial photos with data gathered from city agencies, utilities, and developers, and will be continuously updated in years hence. While the New York map will be in some ways a very jazzed-up version of a traditional map, the Los Angeles product will be more of a virtual city, allowing users simulated strolls through various neighborhoods.

"It will seem like a video game," says Bill Jepson, project director of UCLA's Urban Simulations Laboratory in the Department of Architecture and Urban Design, where the map is being developed. "You'll move your mouse to decide where you want to go, to swoop down from an aerial view if you want, to street level. And you'll see everything from the signs in the shop windows to the graffiti on the wall."

The Virtual Los Angeles effort began in earnest in the wake of the 1992 riots that devastated much of the inner city. (The first use of aerial photos taken for the New York map was for police planning for what was only a cultural cataclysm: a 1996 Garth Brooks concert in Central Park.) "There was work being done long before the riots, but that was what focused attention on it," says Jepson. Many officials expected that some neighborhoods would be radically reconstructed. In fact, the changes were slight -- Magic Johnson movie theaters went up and some liquor stores were pressured not to reopen -- but by then other benefits from detailed mapping and real-time simulations had emerged. Uses for the data in either city could range from shaving 15 minutes off your commute with Web cam traffic previews and "smartcar" navigation to avoiding an American Bhupa with the movement of a plume of hazardous gas anticipated and routes for evacuation and emergency-team access established. Advocates say that the extremely detailed presentations will also aid water management, architecture, civil engineering, and tourism. .

New York's mapping effort was begun by the New York City Department of Environmental Protection, which continues to push it as part of its mission to protect water supplies for nine million urbanites and upstate residents in a 2,000-square-mile area. For years, the city has used geographical information systems (GIS) and computer-aided design (CAD) technologies to chart its land. In the 1980s, the DEP took on a water-mapping project that consisted of converting records on three watersheds, 23 pollution-control facilities, 19 reservoirs, three controlled lakes, 6,000 miles of underground sewers, and one million building connections.

The U.S. Geological Survey supported earlier mapping and spatial analysis efforts with small-scale datasets. But the New York DEP lacked a highly accurate photogrammetric land base -- aerial shots with topographical contours and spot elevations. The Bureau of Water and Sewer Operations agreed to fund the collection of that data in 1996, and other city agencies soon jumped in to integrate their datasets with those built by the DEP, which commissioned Hunter College's geography department to maintain the map for at least the next four years, according to Alan Leidner, director of the project at the City's Department of Information, Technology, and Telecommunications (whose acronym is pronounced "do it.") The base map now occupies 50 gigabytes. But it will grow as utilities, other companies, and public agencies integrate their maps and data into it, Leidner says. In order to ensure that accurate, updated data continues to flow in, Leidner hopes that digitizing plans will be a requirement for obtaining a permit for construction.

The New York map, since it is a public endeavor, will likely be available for free on the Internet. "There's been a bit of a debate about that," says Leidner. "Some people say that since we've poured millions and millions of dollars into this, we should try to get some of that back. But a lot of other people think that this kind of comprehensive information base, if made free to anyone who wants it, would make New York a better place to set up and do business. That, of course, would increase the tax base and we'd benefit from that."

THE SPRAWLING LOS ANGELES MAP, on the other hand, is being generated by a small team of researchers at UCLA, and funded and developed in a "checkerboard" fashion. "No one is going to do it in one fell swoop," says Jepson. "You fill in one square and move on to the next. It's not really slowing us down to do it that way. The demand from the city and from developers guarantees that we'll be busy again as soon as one particular section is completed." Tiles are done as requested. But that doesn't mean that the rich will get served first. Developers can contract to have their property surveyed, but for equal money the city can apply the same level of diligence to lower-income housing. Where money does come in, however, is in the vending of information. After squares are completed, the information will then be sold to new users, says Jepson -- with income put toward further mapping. "If we start giving things away, we won't be able to complete the project," Jepson explains.

Because the Los Angeles map is designed to reflect the pulse of the city, and not just the layout of its arteries, the mapmakers are seeking ways of tracking traffic flow. To get a better idea of how cars move through Los Angeles during different times of the day, the project organizers are fitting tracking devices on 750 vehicles that make regular rounds through the city. The New York team plans to webcast traffic snarls leading up to the Queensboro Bridge.

Partners and innovations will likely be needed on both coasts as the data piles up, confronting designers with processing limits, tight bandwidths, network lag, and the quirks of maintaining their work on the Net. And there's plenty of need for creative research in both cities. Data needed for a comprehensive map is now scattered among specialists in particular fields. It might be obvious to go to the Department of Transportation to get street widths and centerlines, but who knows all of their elevations? "Well, sewers don't generally work well if they run uphill," Jepson notes. The Department of Sewers and Sanitation came through with the information.

Old-fashioned human eyeballing also plays an important role: New York City's team had to identify and classify "exotic features" like playgrounds and parks situated on the roofs of sewage plants overhanging the Hudson River, and various other oddities, says Leidner. The DOITT group also had to eliminate complicated crisscrossing shadows in aerial photographs, lest they condemn future generations of users to squinting and headaches.

Some of the distinctions Leidner had to make veered toward the absurd. The project's mission statement called for the inclusion of driveways over 200 feet long, but many driveways aren't simple straightaways. And what do about "daisy chain" driveways that linked parking lots, a feature whose capture wasn't required? "When it came to driveways, we were like Eskimos with words for snow," Leidner sighs.

WITH SUCH PRECISE MODELING of two cities (conceivably from skyscraper observation decks down to geological faults) that for some epitomize all that's evil about America, the elephant you may have noticed in the virtual room is terrorism.

Special Agent Ramiro Escudero of the Federal Bureau of Investigation's Los Angeles field office is concerned. The FBI moves to prevent terrorism by obtaining arrest warrants based on "overt acts" or a "totality of circumstances" indicating a clear intent to harm, Escudero said. That can be a suspect's reviewing of detailed maps at a library, staking out traffic patterns, and other on-site preparations. But a simulated city could provide one-stop shopping for such activities in the privacy of a dark room.

"Criminals always use technology to further their activities," said Escudero, who wasn't aware of the UCLA project. "This [detailed map] makes it easier for them to do something." The FBI will step in to bar advanced map makers from including floor plans to federal buildings like the one in Westwood, Escudero said, but otherwise won't be asking the mapmakers to hand over client lists.

"The question is, How do we investigate somebody without violating their rights? There's a fine line between what's protected by the first amendment and what's not," Escudero explained. "If we go too far, people say we're being Big Brother. If we are too conservative and something happens, they'll say, 'Why did you move so slowly?'"

But even a video game maker could conceivably produce a virtual-reality program, call it "I'll Torch Manhattan," and inspire maladjusted copycats. How can the data be safeguarded from abuse? UCLA's Jepson has his hand on the information tap. "I consider that on a one-off basis. While we want this to be pervasive and it has to be self-supporting, so far none of the applicants have been so objectionable we've had to turn them down."

If click New York becomes as friendly to pedestrians and vagrants as brick New York, protecting vital assets will be trickier. "If there's a substation we know is providing power to the whole financial district, we might not want to provide directions to it," Leidner says. And the host computer of the map itself won't be labeled. "We'd like to keep that at least a little bit hidden, I would think." But some things could still be identifiable to the trained eye if left unaltered. "We don't know yet what the fudge factor is going to be," Leidner says. One can almost imagine that substation showing up as yet another Starbucks in the virtual Downtown.

Another fear, perhaps far more realistic than the scenario of a Columbine High School writ large, is the potential loss of privacy -- something city dwellers feel intensely already. Your Community Board, or even prying neighbor (or a few million of them), will get a peak over those hedges and fences. Think twice before building your own sundeck without a permit; likewise, "if you have an illegal chop-shop that's a fire hazard, that will get noticed," Leidner says. "But I don't call that Big Brother. I call that good government."

Erik Baard is a freelance writer in New York.

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