An automotive GPS navigation system can be only as good as its map database. In general, GPS manufacturers don't develop their own mapping and POI (Points of Interest) data, but rather license it from one of two major companies: Navteq and Tele Atlas.

Keeping a map database up-to-date is a daunting task. Recently, I had the opportunity to see firsthand how Tele Atlas updates its databases.

The Tele Atlas Mobile Mapping van that I rode in is a bright orange 2006 Toyota Sienna emblazoned with the company's logo and its tag line, "We're mapping your world." Four high-resolution cameras and a commercial-grade GPS antenna sprouted from the van's roof.

Inside the van, one of the rear passenger seats had been replaced with a rack containing a large battery, a power supply, a computer with a terabyte of storage, and an OmniSTAR differential GPS receiver.

Phil, a senior local data collector for TeleAtlas, and his partner, Luis Coba-Cetina, explained that this van—like nine other identically equipped vans around the United States—is assigned to a highway attribution project. The scope of the project is to survey 170,807 miles of limited-access highways, access ramps, and adjacent streets.

Each data collection team receives its surveying assignment in a data file. The file, when loaded into Tele Atlas's proprietary Vision software, displays each road to survey. One person drives as another team member collects data. As they drive, each of the high-resolution cameras captures a still image every 10 meters. Using these geocoded images, data analysts at Tele Atlas can enrich their limited-­access highway data with information such as splits in the highway, car- or truck-only lanes, HOV lanes, time-related information for HOV lanes, exit numbers, sign locations, and restricted-speed areas.

Tele Atlas has also deployed a fleet of 49 Honda CRVs with GPS-enabled computers loaded with ­Vision software. The Vision software lets the data collectors in the field submit changes to the mapping database based on new or corrected data.

So if by chance you encounter a bright orange Sienna Mobile Mapping Van or one of the Honda CRVs, be sure to give them a friendly wave. They are out there mapping your world for you.

Craig Ellison is PC Magazine's lead analyst for GPS Navigation.