iPhone: GPS vs. Triangulation vs. WLAN – Wrong location due to WLAN / WiFi

Location with WLAN switched on

Knowing where you are is one of the essential things in urban life and web 2.0. Some weeks ago, I was using Google Maps on my iPhone. And guess what, it was locating me at a completely wrong position. Instead of being located at my new offices location, the iPhone located me 1 km north-east, at my old offices location. And judging it from the size of the blue circle around the location, it was pretty sure it would be right. Well, how could this be?

Since the introduction of the iPhone, almost all phone manufacturers provide some kind of functionality to locate yourself. Though many of us think this is always done by using the well-known GPS, this is is not really true. Even in case a mobile phone has a GPS receiver, is it not 100% sure that it can be used to determine your position. GPS tracks down your position by connecting to satellites. But you need a connection to at least 3 GPS satellites, to get some meaningful information on your position.This works best, when the phone is located under a clear sky. In cities or even houses, this is not really possible. So there is a fallback solution called „Assisted GPS“ (AGPS). This simply means: In case it takes too long to find a real GPS connection, there are some fallback meachanisms.

The first fallback is called „triangulation“. When a mobile phone is connected to a network, it is always connected to a signal providers antenna. Depending on the signal strength, you can determine how far the phone is away from that antenna. If in reach of three different antennas, the phone can approximate where it is located. It still does not know EXACTLY where it is, but it can make an educated guess.

The second fallback is wi-fi (WLAN). Most modern mobile phones support these wireless network connections and always scan for available WLAN networks. This is great for positioning: If you are in reach of a WLAN hotspot and you know where this WLAN hotspot is located, you know where you are. When Google was sending around his streetview cars in Germany, it was also detecting wireless networks – and mapping their global position. So with this data, you can also make an educated guess where you are. It is even more accurate than the „triangulation“ explained before,  since the signal reach of a WLAN is much less (200m?) than a mobile phone providers triangulation area (~2km).

Location with WLAN switched off (only Triangulation used)

Where it breaks
The only problem: A network providers antenna is always located at the same position. WiFi routers might not. Last spring we moved office. The new building is built with a lot of steal, not really good for signals coming through. So there is a very bad GPS connection, the phone connection is also not so well. So my iPhone falls back to WLAN detection. Looks like on my iPhones „World WLAN map“ my office WLAN is still located at our old location and they did not do any updates so far.

So the whole fall-back plan is working fine, until people move house/office and take their WLAN routers with them. Let’s hope that the iPhone software is clever enough to trust the „more accurate“ WLAN data only in case its‘ estimated location is WITHIN the „less accurate“ triangulation location. – Otherwise you and your WLAN router might move to Japan, and your iPhone still thinks it is located at home.