As location becomes an increasingly important part of mobile and Web applications, it's useful to know what kind of accuracy, start-up times, and battery life impact you can expect from the location detection technologies that are out there.
|Technology||Accuracy||Positioning Time||Battery Life|
|GPS||10m||2-10 minutes (only outdoors)||5-6 hours on most phones|
|WiFi||50m (improves with density)||Almost instant (server connect & lookup)||No additional effect beyond WiFi connection|
|Cell tower triangulation||100-1400m (based on density)||Almost instant (server connect & lookup)||Negligible|
|Single Cell Tower||500-2500m (based on density)||Almost instant (server connect & lookup)||Negligible|
|IP Address||Country: 99% accuracy|
City: 46% US, 53% Intl
|Almost instant (server connect & lookup)||Negligible|
Most laptop/desktop computers can use WiFi and IP to locate their position. But newer laptops also have GPS capabilities. Most smartphones are able to use a hybrid of GPS, Wifi, and cell tower triangulation to locate themselves. CEO of Skyhook Wireless, Ted Morgan, shared some additional insights on how mobile devices locate themselves.
"Two-thirds to three-quarters of the time, he says, when the iPhone locates itself, it's doing so using the Skyhook Wi-Fi geolocation software built in to the phone, and not GPS.
There are several challenges with GPS, it doesn't work indoors. It's also slow, even when it does work. "Time to fix" for a device that's been powered off is 30 seconds at best, and for instant-on, quick-grab apps like you have on a smartphone or Netbook, that's just too slow. Furthermore, the bigger the screen of a device, the worse the GPS reception gets. Dedicated GPS devices, like dash-top navigators, also have antenna devoted to GPS, but phones in particular give priority to telephone communications and short-change their GPS antenna designs.
When you're out of Wi-Fi range or moving fast (driving), or have a device that is continuously powered-up, GPS works well. That's what it was designed for.
If you are interested in more details on the differences between these location detection technologies, Phil Hendrix's Location Determination Methods: Strengths and Weaknesses is a good place to look.