FOR a phone to get a fix on where it is, it must be communicating with cell towers, Wi-Fi access points or GPS satellites.

The data derived from these communications signals will then be used to determine where the phone is - and where you are.

In some devices, all three positioning methods are used together for more accuracy. Once a location has been pinpointed, the data is then shared with the location-based applications.

Cell towers

As mobile phones typically connect with the cell tower closest to it, knowing which cell tower a phone is connecting with will give a rough location of the phone.

For greater accuracy, some networks even measure the phone's distance from a few cell towers, then measure the signal strength and triangulate them to get a more exact location.

A phone can also determine its own location via cell towers.

Software built in some phones can estimate its distance from a cell tower based on the strength of the signals being sent. This information is then sent to a server that crunches the data and uses it to pinpoint the phone's location.

Hot: Works virtually anywhere since mobile phone signals can penetrate buildings and are not affected by bad weather.

Cold: Not very precise.

Wi-Fi

Companies such as United States-based Skyhook provide their technology for customers like Apple for its iPhones. Skyhook maps out the hot spots by driving around cities and picking up the signals sent out by the Wi-Fi routers and maintains the database.

The access points are constantly sending out signals, which Wi-Fi-enabled phones can pick up.

The phone will then send the information it has sniffed out back to location servers. The servers then use it to determine its location by measuring the signal strength and matching that against the database of hot spots. This information is then reported back to the phone so it knows where it is.

Hot: Works indoors and outdoors and is quite accurate in built-up areas with a high density of Wi-Fi access points.

Cold: Unlike cell towers that stay in position for years, routers are moved around, so Wi-Fi hot spots are constantly changing.

GPS

Global positioning system (GPS) satellites in space broadcast signals that are picked up by the GPS receivers in a phone. The signals hold information about the satellites' location in space. A phone receiving this data can assess where it is in relation to the satellites.

Hot: Most accurate.

Cold: Needs to have a clear line of sight between satellites and phone to work. Dense foliage, buildings and clouds can obstruct GPS signals.

This story was first published in The Straits Times Digital Life.

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