David Janes' Code Weblog

June 27, 2009

How iPhone OS 3.0 delivers location services

iphone,maps · David Janes · 6:38 am ·

Alec Saunders has a seriously cool article on his blog about how your iPhone knows where it is. I got to experience how well this works yesterday when we used TimmyMe in the McCowan Road/Ellesmere Avenue neighborhood to grab a coffee pre-meeting:

Many folks assume that iPhone’s location services are GPS based. In fact, they’re not. […]

Skyhook’s innovation is to augment that with WiFi hotspot locations. Why WiFi? It can be wonderfully accurate, to within 30 to 60 feet, or 10 to 20m which is roughly the same as GPS. WiFi can establish a fix within less than a second. And, WiFi is not vulnerable to overhead obstructions, so it can be used indoors.

Skyhook’s technology relies on a database of WiFi access points in over 2,000 cities (and growing). Much like Google, they use vehicles to drive cities, and using a laptop in the vehicle, they chart the location of WiFi access points. In addition, on iPhone as users use the mapping application, new locations and newly discovered WiFi access points are automatically added to the database. It’s a kind of automated crowdsourcing, based on usage.

My emphasis on that last sentence. Very cool.


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