Youre jogging in New York Citys Central Park when you spot a dead crow on the grass. Back home, you visit the city health departments West Nile virus information Web page to report the sighting.

A year ago, you might have added a sentence describing where in the 843-acre park you found the possibly infected bird. This year, you locate your jogging route on a map and click the spot where the crow lay. Your input, translated into spatial coordinates, instantly updates the Health Departments database of dead birds. As more citizens enter or phone in reports, workers know exactly where to retrieve the feathered corpses for testing, and the database generates a map to help the department track the spread of the disease.

The difference between summer 2000 and summer 2001 is that the New York City Department of Health has linked its West Nile virus information system to NYCMap, an interactive geographic database that encompasses the entire city and is accurate to within one foot.

"You can see manhole covers. If you go to Yankee Stadium, you can see home plate," said Mario Merlino, director of policy and planning and head of the geographic information systems (GIS) unit at the Department of Health. With that level of detail, citizens can also precisely report standing water in which carriers of the virus -- mosquitoes -- might breed, and city workers can identify duplicate reports so that they dont drive out twice to treat the same puddle with larvacide.

Piling Up Data

New York has spent the past seven years developing NYCMap (pronounced "nice map") as a common, highly accurate platform for geographic data maintained by city agencies. Some agencies already use it internally. But its only now that ordinary citizens have been able to see its benefits first hand. The West Nile virus-reporting form is one of the first public applications tied to the database, but many more will follow.

NYCMap was born in the citys Department of Environmental Protection (DEP), which wanted to link digital maps of the citys water and sewer infrastructures to a map of physical features. The result would show precisely where the water and sewer facilities stood in relation to one another and to points on the earth.

The concept soon broadened. "Once you created an accurate physical base map, it made sense to consider having that as the standard for the whole city, for any map-making activity," said Alan Leidner, director of citywide GIS at the New York City Department of Information Technology and Telecommunications (DoITT). By linking all of its maps to the base map, the city government could "start to build a GIS data utility, where all the citys graphical and attribute geographic information could be piled up and used interchangeably."

The base map, developed from approximately 7,500 aerial photographs encompassing the entire city, took about three years to complete. It includes an orthophotographic view -- a processed and digitized version of the photos fused into a seamless map -- and a planametric view -- an array of planes and outlines so detailed that one can see individual spaces in a parking lot. Every point on the map matches its position on the earth to within two feet, and the distance between any two points on the map is accurate to within one foot.

Although the base map charts the lay of the land in exquisite detail, it is merely a picture without data from other sources. To add intelligence to NYCMap, city agencies are busy aligning their own geographic data to the foundation.

City Planning, for example, is registering its large and well-established database of street centerlines, address ranges and related information to NYCMap. That project should be finished next spring, according to Richard Steinberg, director of geographic systems at the citys

Merrill Douglas  |  Contributing Writer