It's late on a Friday morning, and Mark Chillanis is dodging backhoes and cement trucks on a road winding through yet another expensive new development on the outskirts of San Francisco.
As his late model Ford Taurus rounds a fresh patch of roadway with a distant view of the San Francisco Bay, Chillanis glances periodically at the screen of a laptop beside him, where a bold line maps a trajectory of the car's path. The line, superimposed over a street map of the city, is a direct feed from a conical satellite receiver fixed to the roof of the car, which measures the car's location each second by global positioning satellites.
Although the street on which the Ford is driving already shows up on the laptop screen, the GPS data shows that the mapped image is about 50 feet off from where the road actually is. Chillanis says such discrepancies aren't uncommon when he's verifying data from maps provided by the local county Assessors office.
"The assessor's map comes out before the real construction," said Chillanis. Oftentimes, the layout of a finished development is slightly different from the plans originally submitted to county officials.
As a field analyst for Navigation Technologies -- a company that develops road databases for use in online and in-car mapping services -- Chillanis spends a lot of his time checking the accuracy of older maps. He typically spends a couple of days a week on the road, gathering GPS data for new developments and public roads throughout Northern California.
Chillanis is one of more than 400 field analysts who drive several million miles of roads each year and feed their findings into Navigation Technologies' database. The mapping data is licensed to several navigating services, including MapQuest, Yahoo Maps and General Motors' OnStar in-vehicle navigating system.
In addition to the satellite data, field analysts also make notations onscreen about roadside information relevant to drivers seeking the quickest way to their destinations. These include information about U-turn signs, road dividers and left-turn markers, as well as points of interest like hotels or public transit stations.
While mapping data is still sometimes error prone, as many misdirected users of MapQuest can attest, companies that use the information say things have been improving in the last several years.
Geri Lama, spokeswoman for OnStar, recalls problems reported in the early days following the service's 1996 launch. Some drivers even complained that a route listed as a road was actually a railroad track. Lama said it's been years since she's heard of a routing error like that happening.
For Navigation Technologies, a privately held company in Chicago, the effort to expand coverage has required many staff visits to out-of-the-way places. Matt Krause, area manager for Northern California, tells of being stuck in the mud, dodging deer and getting caught in a freak summer snowstorm. Others get the cushier assignments, such as a recent trip to map several Hawaiian Islands.
Prior to 2000, Krause said, much of the job involved marking up paper maps with pens. No more. In addition to a GPS connection, in-car laptops come equipped with an audio program that allows drivers to record a roadside feature, such as a no-left-turn sign, and store the data at the exact map location when it was passed.
The GPS receivers themselves, though fairly compact, have also generated some attention from less tech-savvy observers.
"I've had people stop to say "You've got a lamp on your roof. You're driving away with a lamp. I say no, but thanks," Krause said.
