They match map points with locations in anything from police blotters to real estate listings.
SAN FRANCISCO -- Tracking sexual predators in Florida. Guiding travelers to the cheapest gas nationwide. Pinpointing $1,500 studio apartments for rent in Manhattan.
Geeks, tinkerers and innovators are crashing the Google party, having discovered how to tinker with the search engine's mapping service to graphically illustrate vital information that might otherwise be ignored, overlooked or not perceived as clearly.
"It's such a beautiful way to look at what could be a dense amount of information," said Tara Calishain, editor of Research Buzz and co-author of "Google Hacks," a book that offers tips on how to get the most out of the Web's most popular search engine.
Yahoo and other sites also offer maps, but Google's four-month-old mapping service is more easily accessible and manipulated by outsiders, the tinkerers say.
As it turns out, Google charts each point on its maps by latitude and longitude -- that's how Google can produce driving directions to practically anywhere in the nation. Seasoned developers have figured out how to match these points with locations from outside databases that can contain vast amounts of information -- anything from police blotters to real estate listings.
Thanks to Adrian Holovaty, 24, who overlayed Chicago Police Department crime statistics on a Google map, house-hunters in the Albany Park neighborhood can pinpoint all the sexual assaults in the district between May 19 and April 19 on a single map. With each crime marked by a virtual pushpin, Chicagoans can quickly learn what dangerous train stations, pool rooms and alleys to avoid.
Holovaty hopes to make the maps more current by persuading Chicago police to provide the data directly, rather than forcing him to glean it from the department's Web site. Police seem amenable -- he's got a meeting with them next week. But community activist James Cappleman is already impressed with Holovaty's Chicagocrime.org -- no longer do people have to trust politicians crowing about safer streets.
"We've never been able to track trends before," Cappleman said. "Now, when we tell police there is a problem, we'll know what we're talking about."
Visitors to Floridasexualpredators.com, which combines Google Maps with data on convicted sex offenders, can call up maps of their communities and click on the pushpins to see the name, last known address and mug shot of each offender.
Drivers searching for their area's cheapest gas can go to www.ahding.com/cheapgas, which blends Google Maps with data from Gasbuddy.com's database of prices at individual gas stations.
Home buyers can pinpoint the locations of houses in their price range at Cytadia.com. And renters can turn to Housingmaps.com to spot available housing in 29 cities including San Francisco, New York, Los Angeles and Chicago.
All these sites are operating without Google's permission, clearly violating the company's user agreement. But none charges any fees, and Google, which declined to comment, has made no effort to shut them down.
"Why would they?" asks Kenneth Tan, who works for a Chicago-based media research firm and is relying on Housingmaps.com to find a new place in New York. "This is fantastic publicity for the company."
Before Housingmaps.com launched in March, Tan spent up to 30 minutes a day reading through Craigslist postings in his price range, trying to figure out if any were located where he wants to live.
On Housingmaps.com, the listings he wants are represented on a single map, marked by either a red or yellow pushpin symbol. Yellow come with apartment photographs; red have none. A click on a yellow pin sends Tan directly into the Craigslist posting on the street where he hopes to live.
"It takes two seconds to glance at the map to see if there is anything for me that day," Tan said.
Computer animation engineer Paul Rademacher developed Housingmaps.com shortly after Google Maps launched in February, matching it with all the U.S. apartment listings on Craigslist. He says he was intrigued by Google's technology and began tinkering with it after a long apartment search.
James Brown, founder of Floridasexualpredator.com, charted the home addresses of every registered sex offender in Florida's Megan's Law database, then wrote a software program that automatically converts addresses to the correct latitude and longitude.
Holovaty requested data from Chicago Police but never heard back -- so he wrote a program that automatically retrieves crime location data each time the department's Web site is updated.
Why go to this much trouble?
The site's creators said it was for the love of discovery and a chance to help their communities.
Brown came up with the idea for his site after watching television reports about a kidnapped girl with his father, a former policeman in Ocala, Fla. Rademacher says he wanted to help others avoid painstaking and time-consuming searches for new apartments.
"I figured out a way to do it and I didn't see any reason why I shouldn't share it with everybody," said Rademacher, who lives in Santa Clara.
None said they did it for the money. But their efforts are certainly getting attention.
Several companies have approached Rademacher about setting up other sites that marry data to Google maps. And San Francisco is among cities interested in whether Holovaty can develop crime-mapping sites for them.
"I would be happy to help them set it up," Holovaty said. "The world is a better place whenever you provide more information."
On the Net
Crime locations: www.chicagocrime.org
Sex predators: www.floridasexualpredators.com
Cheap gas: www.ahding.com/cheapgas/
Great apartments: www.housingmaps.com