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There are three ways smart phones and tablets can determine location.

  • GPS - Global Positioning System - Accurate to 10-50 ft.
  • Wi-Fi signal triangulation.
    Google built a database of Wi-Fi SSIDs (network name) and locations through their Street View project, so when you drive by a location with a detectible Wi-Fi network it knows where you are.
    Wi-Fi hot-spot triangulation is a commonly used method of determining location on modern smartphones, as GPS doesn't always work in urban locations and cell-tower positioning can be inaccurate.
    See: CNET News
  • Cell-tower - triangulation.
    By measuring signal strength, the round-trip signal time and sector location (see diagram below) you can be located in a pie shaped wedge from the tower. Doing this for 2 or more towers the phone can determine where you are in relation to the towers.
    See Cell Phone Triangulation Accuracy Is All Over The Map at SearchEngineLand.com

 

See Cell Tower Triangulation - How it Works | Wrongful Convictions Blog

The antennas on a cell tower are always arranged in a triangle. Each of the three antenna arrays covers a 120° sector with the tower at it's focus, and these sectors, by convention, are referred to as alpha, beta, and gamma - α, β, γ. a cell tower can tell from which of the three antenna arrays it is receiving a signal.

Using cell tower triangulation (3 towers), it is possible to determine a phone location to within an area of "about" 3/4 square mile.


Google Maps on phones doesn't use triangulation but the signal from one tower and doesn't seem to distinguish which sector it's in.

In driving around my suburban neighborhood with an android tablet with GPS turned off this produced circles on the map with a radius of from about 1/2 mile to 1 mile and as I passed a Wi-Fi hotspot it knew about it would get within 100 ft.

In suburban areas towers are usually spaced every couple of miles.

Map of towers in my neighborhood.

Source: AntennaSearch.com

Links:
Google mobile apps collect Wi-Fi location data | CNET News
Cell Phone Triangulation Accuracy Is All Over The Map at SearchEngineLand.com
Cell Tower Triangulation - How it Works | Wrongful Convictions Blog
Apple - iPhone 4S - See the best way to go with Maps and Compass.
AntennaSearch - Search for Cell Towers, Cell Reception, Hidden Antennas and more.

last updated 1 June 2012