Having your phone know where you are and what you're doing is one of the creepiest but most useful aspects of modern smartphones. From Google Now to location-based notifications on iOS, you probably take advantage of it every single day. But how does it work, and what's going to happen in the future?
At the moment, smartphones routinely use two technologies to check on your whereabouts: the American-made Global Positioning System (GPS), and the far more mundane Wi-Fi.
GPS, as you may already know, works off satellites: a constellation of 24 American-military-owned satellites, orbiting around the Earth, can provide an accurate location fix to any GPS receiver that can 'see' a minimum of four satellites. The mechanics of the location system rely on Einstein's theory of relativity and hyper-accurate atomic clocks on board the GPS satellites to calculate the receiver's distance from the satellite using radio waves; once the receiver has worked out how far it is from a minimum of four satellites, it can work out its own position to within a few metres.
But GPS isn't the only show in town when it comes to satellite location. There's also systems built or in development from the Russians, Chinese, Indians, and even our own EU.
After the Americans, the Russian system is the next-most advanced. Called GLONASS (which stands for Global Navigation Satellite System in Russian, apparently), it also consists of 24 satellites, giving it the same kind of global coverage as GPS.
It was first operational in the mid-'90s, but fell into disrepair around the turn of the century, falling to just six operational satellites. Thankfully, everyone's favourite Russian leader took the programme under his wing, and in April this year, GLONASS was restored to its full complement of 24 satellites.
In line with the rise of GLONASS, smartphones have started to offer it as a compliment to GPS. Since the iPhone 4S, Apple products have been rocking a GLONASS-enabled chipset, and all the top-end Android phones available at the moment have GLONASS capability.
That's because of two reasons -- firstly, having GPS and GLONASS is better for you and me, since it means you're more likely to get a signal. But additionally, Russia has a 25 per cent import tax on non-GLONASS enabled products; that would destroy sales of any product, and as a result, major chipset manufacturers like Qualcomm and Broadcom have started sticking GLONASS in by default.
There's other satellite navigation programmes. Galileo, the European effort, promises to be even more accurate than GPS or GLONASS when it comes to fruition, but at the moment, it's running vastly over budget and behind schedule (it is an EU project, after all).
The Chinese system, BeiDou Navigation Satellite System (or BDS for short), is semi-operational. It has coverage of China and the surrounding area at the moment, with planned full-globe coverage currently under construction. It offers capabilities on par with GPS, and is mostly being constructed in order to allow China's military arms independence from GPS.
Satellite systems, in all their different guises, are pretty neat -- universal coverage, low user cost and simplicity are pretty good traits. But sadly, using GPS on a phone to work out location will burn through your battery in an hour or two.
That's why phones also use Wi-Fi to work out location. Thanks to a couple of vast databases that cross-reference Wi-Fi network data with geographical location, your smartphone can normally work out where you are in the world in under a second, just by looking at what Wi-Fi networks you can see.
The data for these databases is collected either through 'wardriving' -- cars with Wi-Fi antennas driving around, collecting the data -- or, more commonly, by using every smartphone on a given platform. So, when you have GPS and Wi-Fi switched on on your handset, it's quite possibly gathering data about nearby Wi-Fi hotspots and phoning it home. (This is what Google's currently in hot water about, since its StreetView cars used to collect more than their fair share of data from unprotected Wi-Fi networks when they were driving around.)
This combination of GPS and Wi-Fi data makes a potent pair. Generally, if you're in an urban area, indoor or out, your phone will be able to pinpoint where you are to within a tennis-court-shaped area, at worst.
But for many applications, a tennis-court-shaped-area isn't enough. That's why some companies are working on pinpoint indoor navigation -- with or without your consent.
Some companies -- the US-based RetailNext and Nomi, to single a few out by name -- passively track customers in stores over Wi-Fi, without their consent and without them being connected to Wi-Fi. Just by the act of having your Wi-Fi chip turned on and scanning for signal, your position can be triangulated and logged -- meaning that the companies can pick up data on how often you visit the store, and what times, and what sections you loiter in most.
But there are other, less creepy, tracking alternatives around. One of the most intruiging is Open Positioning System (OPS), a concept that wants to use seismic signals (like those generated by turbines or power stations) to triangulate location, thus avoiding any kind of expensive satellite system. The idea, developed by a student at the Royal College of Art, is still in beta testing, but seems promising, at least for static systems -- you don't want to have to put your phone on the ground to work out where you are.
OPS isn't the only system trying to use existing infrastructure for location systems, either. BAE Systems has a research project to use a mixture of signals -- GPS, Wi-Fi, cell towers and TV signals, for example -- to get a precise location. The advantages of that approach are clear -- no new infrastructure, and a range of frequencies meaning that the coverage would likely be pretty comprehensive. However, multiple frequencies also means multiple receivers, which drives up the bulk and cost -- not something popular with smartphone manufacturers.
Either way, advances in location technology are coming. One of the themes of recent smartphones -- the Moto X and iPhone 5S particularly come to mind -- is a refocus on contextual computing, with handsets increasingly aware of their whereabouts. Knowing the geographical location is a key cornerstone of contextual computing, and with only an imperfect, battery-hungry system in place at the moment, changes are sure to come thick and fast.