Skyhook now employs a fleet of 500 drivers to feed a database that spans North America, Asia and Europe. The landscape of signals changes constantly as people and businesses set up and take down wireless networks, so the scanning process never ends.

Each Skyhook car contains a laptop outfitted with antennas and equipment that sends out short blasts of radio waves, called probe requests, to detect nearby cell towers and Wi-Fi networks. The system calculates the source of the signals based on their strength and the location of the car. That information is logged in the Skyhook database, which includes more than 100 million wireless networks and 700,000 cellular towers.

Skyhook’s big break came in August 2007 when Steven P. Jobs, Apple’s chief executive, requested a meeting with the company. Mr. Morgan said he initially deleted Mr. Jobs’s voice mail message, dismissing it as a prank, but soon realized his mistake.

Since then, Apple has sold 37 million iPhones and iPod Touches worldwide, all with Skyhook’s software on them. Mr. Morgan declined to detail specifics of Skyhook’s financial agreement with Apple, other than to say that his company collects a commission for each device sold.

When an iPhone owner starts up an application that involves location  like the restaurant finder Urbanspoon or the forecast service WeatherBug  the phone calculates whether it is likely to get the best and fastest information from its own GPS chip or from Skyhook’s system. Skyhook says it can provide a fix on location in seconds, versus up to a minute for GPS, although Skyhook is less useful in areas with few Wi-Fi networks.

Skyhook checks a list of nearby Wi-Fi access points and cell towers against its database and triangulates the device’s location within 30 to 60 feet. The company says it is not connecting to those Wi-Fi networks, just detecting their presence. (As a backup, the iPhone can also use cell tower information from Google.)

Any new access points and cell towers detected by the iPhone are automatically added to the Skyhook database, making it, in Mr. Morgan’s words, “self-healing.”