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I have used "Find my Mac" to find our Macbook Pro. It was pretty accurate and was able to place the computer within 10 feet of its actual location. I started thinking about how it actually works, since the MBP doesn't have a GPS. How does "Find my Mac" work?

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While not worthy of an answer, you can also get location information through ISP routing information, but this is not nearly as reliable (because of switches, network setup, and just distance) and not used for Find My Mac. –  jmlumpkin Mar 24 '12 at 12:33

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It checks what Wifi networks are in range and then looks up their locations in a big database of known Wifi access points -- I think Apple use the Skyhook database.

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Just to clarify. Apple did use the Skyhook database in the past, but these days they have created their own much larger database by croudsourcing from iPhones that happen to be turned on with their GPS active when they encounter any wifi network (without needing to actually connect to the wifi). All of Apple's GPS-equiped devices will also use wifi triangulation while waiting for the GPS to get a fix, and (because wifi is thousands of times faster) to give the GPS chip an approximate location so it can focus on just the last few metres of the location fix. –  Abhi Beckert Mar 24 '12 at 10:02

Wi-Fi Positioning system (WPS)

The Mac can use Wi-Fi network identification for localization. This is called a Wi-Fi Positioning System (WPS). The access points name and signal strength is determined and looked up in a database to identify the location. The more access points are found, the more precise the localization.

Unlike GPS (Global Positioning System) or cell-tower triangulation (together called Assisted-GPS), the Wi-Fi based localization works well inside buildings.

There are different databases which collect wireless access points:

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Even without a GPS chip, your location can be determined using your MAC address, SSIDs of WiFi networks in range (both private and public networks), their signal strength, etc. In Apple’s case, this data is submitted to the Skyhook Wireless service, which then returns a set of GPS coordinates (latitude, longitude).

If you’re interested in how geolocation works in other devices and applications, and what data is being sent back and forth exactly, see this answer on Stack Overflow which explains how Firefox does this using Google’s geolocation service (which is what most other apps use).

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Technically, it doesn't use your MAC address or the access point's SSID, it uses the access point's BSSID - which is the MAC address of the wireless interface. (A router's ethernet interface would have a different MAC address.) –  Jamo yesterday

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