Pinpoint: How GPS Is Changing Our World 
by Greg Milner.
Granta, 336 pp., £9.99, June 2017, 978 1 84708 709 6
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In August​ , a man with a sword was arrested near Buckingham Palace on suspicion of preparing to commit an act of terrorism. Westminster Magistrates Court heard that the man, an Uber driver from Luton, had intended to go to Windsor Castle but his satnav directed him to a pub called The Windsor Castle instead. Without stopping for a drink, he drove on to Buckingham Palace. It isn’t clear if he was still relying on the satnav for the final stage of his journey, or whether rage at the mistake was a motivating factor in his alleged offence. Three police officers were said to have received minor injuries; presumably he hadn’t stopped to ask them for directions.

Greg Milner includes a few stories about satnav fails in Pinpoint, his lively history of satellite navigation technology – his central chapter is called ‘Death by GPS’ – but one of the eye-opening things about his book is quite how far-reaching the tech is. As well as guiding missiles and encouraging motorists not to pay attention to road signs or even to the road ahead of them, GPS is used in crop management, high frequency trading, weather forecasting, earthquake measurement, nuclear-detonation detection and space exploration, as well as the smooth running of countless infrastructure networks, from electricity grids to the internet.

GPS, which stands for Global Positioning System, was developed by the American military. The US Department of Defence currently spends more than a billion dollars a year maintaining it. There are 31 GPS satellites orbiting the earth, all monitored, along with hundreds of other military satellites, from Schriever Air Force Base in Colorado. For the system to work, a receiver on the ground – your mobile phone, for example – needs to have a ‘line of sight’ to at least four of the satellites (there are very few places on earth where it wouldn’t). Each satellite continously broadcasts its position, along with the time the signal left the satellite. The time it takes for the signal to reach you (measured in milliseconds) will tell you exactly how far away it is. Three of these signals provide enough information to pinpoint your position; the fourth confirms the time used in the calculations. GPS satellites, unlike mobile phones, carry super-accurate atomic clocks, which are continually synchronised with one another. This is necessary for the precision of the positioning system, but many of the applications of GPS make use of it primarily as a timekeeping device.

Since 1967, the second has been defined as ‘the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom’. A pendulum clock uses gravity to make a pendulum oscillate at a measurable frequency; a quartz clock uses electricity to make a quartz crystal oscillate at a measurable frequency; an atomic clock uses microwaves to make caesium (or similar) atoms oscillate at a measurable frequency. In the 1970s, the only way to synchronise your atomic clock with the one at the International Bureau of Weights and Measures was to take it to Paris with you and compare them side by side. Now it’s all done by satellite signals. GPS time is also what enables stocks and shares to change hands in microseconds, prevents power surges in vast electrical grids and keeps the internet ticking smoothly.

But before it was co-opted as the pocketwatch of late capitalism – a gift from the US government – GPS was developed as a way to help the US air force drop its bombs just where it wanted with as little risk as possible to American lives. As with any technological breakthrough, it took decades, with false starts, moments of inspiration, patient refinements, scepticism from the brass (‘We’re the navy, we know where we are’), inter-service rivalry and a more or less steady influx of government cash. Within days of Sputnik’s launch in 1957, two young engineers at Johns Hopkins University were using the Russian satellite’s radio signal to plot and then predict its position. GPS came of age in the 1991 Gulf War.

The US air force bought the first GPS-enabled missiles in 1988; new satellites were launched in 1989. There were teething problems: the solar panels on one satellite didn’t work; another’s flywheels were playing up. ‘Technicians opted to put it in a permanent spin,’ Milner writes, ‘that kept it in a position with its antenna pointing towards Kuwait City.’ It was stabilised on 16 January 1991. At 2.30 a.m. on 17 January, six American helicopters took off from a base in Saudi Arabia. The two in front carried GPS receivers; the four behind, Hellfire missiles. Within minutes, two Iraqi radar posts had been destroyed to pave the way for a surprise stealth bombing raid on Baghdad. Milner tells this story with all the skill of Tom Clancy, and quotes with apparent approval the officers who have sung the technology’s praises. General Chuck Horner, who ran the air campaign in the Gulf, was a fighter pilot in Vietnam. He said in his memoir (written with Clancy) that he ‘hated’ his superiors ‘because they asked me to take other people’s lives in a manner that dishonoured us both’. The Gulf War would be different, in part thanks to GPS. Milner doesn’t say whether or not the technology was used on the night of 26 February 1991, in the slaughter from the air of hundreds or possibly thousands of Iraqi conscripts as they retreated from Kuwait along the ‘Highway of Death’.

He acknowledges that the tech isn’t perfect, however, and that it doesn’t ‘eliminate human error’, citing the bombing of the Chinese Embassy in Belgrade in 1999 – the CIA was using an out-of-date map, or so it said – and the unfortunate case of a US soldier in Afghanistan who changed the batteries in his GPS receiver before transmitting the co-ordinates of a Taliban outpost. The first thing the receiver did after being switched back on was automatically broadcast its own position, bringing a 2000-pound bomb down on top of it.

There used to be two different GPS signals: a high-precision one, which only military receivers could decrypt, and a deliberately degraded one for civilian use, which gave your position to within a hundred metres or so. When US troops started shipping out to the Gulf after Saddam Hussein invaded Kuwait in August 1990, they had only 13 Manpack portable GPS receivers between them. Each one cost $40,000 and weighed 12 kg. The Department of Defence put in an order for thousands of Trimpacks, portable receivers built by a former Hewlett Packard engineer called Charlie Trimble (one of the many people Milner interviewed). But there still weren’t enough to go round, so a lot of soldiers ended up spending $1000 of their own money on mass-produced Magellan portable receivers, which were less accurate than Trimpacks but better than nothing in the middle of a hostile desert. The Magellans were made by Ed Tuck, an ex-military venture capitalist with a background in the tech industry. He’d imagined selling cheap (less than $300) GPS receivers to middle-aged men who didn’t like admitting they were lost or asking for directions, but many of his early customers were people with boats off the southern coast of Florida – drug dealers or people traffickers.

Because so many soldiers in Desert Storm were carrying GPS receivers that used the civilian signal, the military turned off the ‘selective availability’ software that degraded it. They turned it on again when the Gulf War was over, but amateur GPS enthusiasts would have noticed a sudden improvement in their receivers’ accuracy in September 1994, when US forces landed on Haiti to depose General Cédras and restore Jean-Bertrand Aristide to power. Meanwhile, commercial GPS receiver manufacturers were developing ways to overcome or work around selective availability, and make their products more accurate in spite of it. In May 2000 the military stopped degrading the civilian GPS signal. Sales of GPS receivers soared.

It isn’t just every phone and every Uber car that’s now fitted with GPS; in some parts of the world it’s every tractor too. And not because farmers need to be reminded of the way to their fields. Milner visited a sugar beet farm in Colorado, a few hours north of Schriever Air Force Base. Using GPS in combination with the Russian glonass system to achieve ‘sub-inch accuracy’, the beet farmer tills his field in strips, leaving a narrow band of fallow earth between each row to help keep water and nutrients in the soil. Each seed is planted in a precise, recorded position, with more of them in the more fertile parts of the field. Just the right amount of water and fertiliser is sprayed onto the beets. When they’re harvested, each and every one can be plucked entire from the earth (a broken beet is no use to anyone). Milner reckons that GPS is now worth billions a year to American farmers. An experiment in Uttar Pradesh, meanwhile, found that levelling the land on a two-acre farm using GPS nearly tripled the wheat yield. The farmer in Colorado told Milner that GPS gives him ‘intimate knowledge’ of the land, like his grandfather, who walked behind a horse looking at the ground beneath his feet. Still, hi-tech agriculture has its downsides. Not so many years ago, it took two men to harvest a beet field: one of them driving the tractor, the other operating the digger at the back. Now the tractor does almost everything itself; the driver merely has to turn it round at the end of the row. Soon, he won’t have to do even that. A former farmhand in East Yorkshire told me this summer that he had stopped driving tractors because he can’t understand the computers.

It isn’t​ only technology that GPS is changing but also, as Milner puts it in his US subtitle, ‘our minds’. Human beings have long had different ways of navigating. Milner follows the distinction made by the aviator Harry Gatty in Nature Is Your Guide (1958) between ‘home-centred’ and ‘self-centred’ navigation. Using the former, you consider your position in a relation to a single fixed reference point. Milner imagines members of ‘the earliest human society’ going out to hunt or gather with a sense of how far they were from home, and in which direction, based on a form of dead reckoning: working out where you are according to how long you’ve been travelling at a known speed (sailors used to have to do it; on the open sea you can’t triangulate your position on a map using fixed reference points because there aren’t any). Milner’s putative hunter-gatherers, for example, might have considered themselves half a day’s walk from home towards the setting sun.

In a self-centred wayfinding system, ‘we define our position objectively, sometimes with help from tools such as maps or GPS, but rarely by where we are in relation to our homes. Dead reckoning is kept to a minimum. The centre of our world is us.’ (You might have thought that was more subjective than objective, but apparently not.) We also use a ‘local-reference’ system, which ‘defines location in reference to a prominent enviromental feature’, such as a mountain, or the Shard. The Polynesians who populated the remote islands of the Pacific in a great eastward migration across hundreds of miles of open water used a system called etak, which allowed them to navigate according to the positions of islands that they couldn’t see but knew were over the horizon. They kept track of them using a combination of dead reckoning and star positions.

In 1948, the psychologist Edward Tolman published an article called ‘Cognitive Maps in Rats and Men’. Watching rats finding their way through a maze, Tolman rejected the strict behaviourist idea that each individual wrong turn was a separate negative stimulus to which the rat responded by not taking it again, and each individual correct turn was a separate positive stimulus to which the rat responded by taking it again, in favour of the idea that the rat was somehow building up in its brain a ‘cognitive map’ of the maze. Tolman distinguished between two kinds of cognitive map: a ‘strip map’ of the correct route through a maze and a ‘comprehensive map’ of the entire maze. If you have only a strip map in your head and stray from the path, you’re instantly lost. And with GPS, Milner writes, ‘the soothing voice of the turn-by-turn directions, guiding us through an unfamiliar environment, is the personification of the strip map.’

There are rare neurological disorders that prevent people from forming cognitive maps, and it seems at least possible that an overdependence on GPS could have a similar effect. A study a few years ago found that London taxi drivers, required to find their way about the capital unaided (no chance of a sword-wielding black-cab driver rocking up outside the wrong Windsor Castle), have larger hippocampuses than most people. (The hippocampus is part of the brain that has a role in, among other things, spatial memory and navigation.) The Knowledge, in other words, may be observable in cab drivers’ brains. It’s hard to know for sure, but it seems at least possible that outsourcing our wayfinding to electronic devices may cause our hippocampuses to shrivel. With Google Maps on every phone, who needs a cognitive map in their brain?

There’s another unfortunate side effect of an over-reliance on GPS for wayfinding: the less we need to develop cognitive maps of our own, the less attention we pay to the actual territory. I like to think I’m usually quite good at finding my way somewhere I’ve been only once before. But last year I drove through Leeds relying entirely on GPS and if I had to do it again without the satnav – even if I’d tried immediately after doing it the first time – I wouldn’t have a clue where to go. I doubt I’d recognise any of the places I drove past, either. Milner cites experiments that suggest this experience is universal. It may help to explain how people can be so apparently idiotic as to be led by GPS over a cliff edge, or to a pub instead of a palace, eyes averted from the real world beyond the windscreen, glued instead to the LCD simulacrum suckered to the dashboard. Government statistics don’t reflect whether or not motorists who use GPS are more likely to inflict death or injury on other drivers, passengers, cyclists or pedestrians on the far side of the glass, but in October last year, a lorry driver was jailed for ten years after pleading guilty to four counts of causing death by dangerous driving; he had ploughed into a line of stationary cars on the A34 while scrolling through music on his phone. It isn’t an isolated case.

Whether or not it threatens our ability to form cognitive maps, or otherwise interact with our surroundings without electronic mediation, GPS is meaningless unless the information from the satellites, pinpointing a position in abstract space, corresponds to an up-to-date map of the Earth. Milner quotes an article by Sameer Kumar and Kevin Moore, published in the Journal of Science Education and Technology in 2002: ‘GPS receivers without GIS have no knowledge of the real world.’ GIS stands for ‘geographic information system’. ‘But to say that GIS helps a GPS receiver know the real world,’ Milner writes, ‘is not quite right. Like any map, the GIS component of GPS offers an actively mediated representation of the world.’ Google Maps, for example, uses the Web Mercator map projection, which like the classic Mercator projection distorts area – making Greenland look much bigger than it is, and Africa much smaller – for the sake of straight lines of longitude. But Web Mercator adds a further distortion by representing the Earth as a sphere rather than an ellipsoid. This causes problems if you want ‘to plot a constant bearing over a very long distance’, but makes no difference if you’re looking for the nearest pizza place. It also saves a vast amount of processing power – calculations involving spheres are a lot simpler than calculations involving ellipsoids – and therefore tens of millions of dollars’ worth of electricity.

In the old days, surveyors would start mapping an area of land from an arbitrary but convenient ‘control point’, whose co-ordinates were 0,0 on the grid, or ‘datum’, that the surveyors projected across the land they were mapping. Jean Picard began his survey of France in 1669 with a 14 km baseline from Paris to Fontainebleau, which he measured using wooden rods. Taking bearings from either end of that baseline, he determined the position of a third point using basic trigonometry: if you know the length of one side of a triangle, and its angles, you can easily calulate the lengths of the other sides. Picard then used those as the baselines of new triangles, and so spread his net across France. He used the results to calculate the length of a degree of latitude. Getting different figures from the north and south of the country, he realised (or discovered, or proved) that the Earth isn’t spherical.

Early surveyors also assumed that the force of gravity was precisely perpendicular to the Earth’s surface at any and every point, but it isn’t, quite, because of the uneven distribution of the Earth’s mass and the remote effects of other objects (such as the Sun and the Moon). This means that a plumb line doesn’t necessarily dangle straight down, and also that astronomical measurements don’t match up exactly to triangulations on the ground. Because different surveyors in different places tweaked things in different ways, their different maps didn’t fit together perfectly. And that’s before you take into account the constant (but uneven) movement of tectonic plates (only confirmed in the 1960s), which means that nowhere on the Earth’s surface stays in the same place. The practical implications of all this incoherence became apparent during the Second World War, when ‘the US army realised that confusion over the various European datums was causing its troops to miss artillery targets.’

In 1960, the Pentagon came up with the first World Geodetic System, a datum covering the whole planet with the centre of the Earth (or nearest estimate) as its control point. Milner calls the WGS ‘arguably the most underappreciated scientific achievement that grew out of Cold War imperatives’. The latest version, WGS84, produced in 1984 and updated a few times since, is what GPS uses for its datum. The position of the Earth’s centre of mass is now known to within 2 cm. WGS84 means the US government is confident its ICBMs can hit the Kremlin or the middle of Pyongyang; it’s also the reason Kim Jong-un is confident he could nuke Hawaii. The system is managed by the National Geospatial-Intelligence Agency, formerly known as the Defence Mapping Agency, which Milner calls ‘essentially the final authority on the GPS data used by everyone’. The DoD calls it a ‘combat support agency’. It controls 11 of the 17 GPS monitoring stations around the globe, including the one in the South of England. Milner repeats a rumour, which an NGA scientist would neither confirm nor deny, that there’s a room at the monitoring station in South Australia which is out of bounds to non-US citizens; it would be amazing if there weren’t.

Information from GPS satellites is used to refine WGS84, which in turn is used to fine-tune the satellites. The system is self-reinforcing at every level: 20,000 km up in the air, the 31 GPS satellites confirm one another’s positions, and metres away from the café in Orvieto where I’m writing this, the tourist in the hire car rolling through the Piazza della Repubblica, eyes on the thick blue line on his satnav, having somehow missed all the one-way and no-entry signs, is sending a signal to Google Maps confirming the misconception that the pedestrian square is a through road.

More serious failures attract the interest of more powerful authorities than the polizia municipale (who aren’t actually bothered by a few stray cars in pedestrian zones). The ‘most dangerous two miles in America’, Milner writes, are along the New Jersey Turnpike where it runs past Newark Airport. Not because of traffic accidents but because of all the ‘critical infrastructure’ and heavy industry, and the size and density of the surrounding population. An explosion at a chlorine processing plant there would threaten the lives of 12 million people. In 2009, Newark installed a ‘ground-based augmentation system’ so planes could land using GPS. The Federal Aviation Authority requires automatic landing systems to be accurate to at least seven decimal places; non-augmented GPS is accurate only to five (99.99999 per cent). But the new GBAS at Newark kept glitching. It took several weeks for the technicians to realise the problem was coming from the traffic passing on the Turnpike. Many commercial vehicles now carry GPS trackers, so companies can keep an eye on their drivers’ movements. But you can pick up an illegal ‘personal privacy device’ that jams the signal for less than $100. Some of the jammers in some of the 100,000 vehicles that drive past the airport every day were inadvertently screwing with the technology that was supposed to make it safer for planes to land there. The engineers adjusted the system’s software to get round the problem, and everything worked OK until a man working on upgrading the runways drove a truck with a GPS jammer into the middle of the airport. He was fined $32,000.

If you can interfere with GPS by mistake, you can also do it on purpose. Todd Humphreys, an engineering graduate student at Cornell, demonstrated to the DoD how (relatively) simple it could be. In June 2012, he and a couple of assistants went with government and military officials to the White Sands Missile Range in New Mexico. They gave a drone flying on autopilot instructions to hover forty feet up in the air, then sent a spoofed GPS signal which tricked it into thinking that it was drifting upwards. (‘Thinking’? You know what I mean.) The drone took evasive action and plummeted to the ground. A year later, Humphreys fooled a yacht in the Mediterranean – he’d been challenged by its captain – into deviating hundreds of metres from its course: spoof the GPS signal, and the crew will steer into your trap for you. The opportunities for hijackers couldn’t be plainer. Once the authorities know how GPS can be spoofed, they can put countermeasures in place, but – as with the eternal struggle between viruses and antibodies – that only stimulates the hackers to find new ways round them. The system, on which so much of modern life that we take for granted depends, is not invulnerable. If it were to fail catastrophically, how would we find our way?

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Vol. 39 No. 24 · 14 December 2017

Thomas Jones refers to our innate capacity for forming ‘cognitive maps’, an aptitude that GPS technology may be eroding at the neurological level (LRB, 16 November). ‘Cognitive mapping’ was precisely the term first used by Fredric Jameson in the 1980s to describe the intellectual activity that would counter the social and spatial disorientation of postmodernity. Jameson saw our spatial confusion as we wandered around metropolises like Los Angeles as a symptom of our inability to grasp the workings of a globalised capitalism – leaving the prospects for concerted political action very bleak indeed.

Jake Soule
Duke University, North Carolina

At the end of a recent satnav car journey my five-year-old grandson, Laurie, asked: ‘Is this our destiny?’

Philip Stevens
Taunton, Somerset

Vol. 40 No. 1 · 4 January 2018

Is Thomas Jones worried enough about the GPS revolution (LRB, 16 November 2017)? Navigators used to have to balance a number of sources of not entirely accurate information in plotting positions, which they marked on charts with a ‘cocked-hat’ of not-perfectly-coincident bearings. To be on the safe side, they always chose an arbitrary position within the cocked hat that was closest to any point of danger. There is an analogy with the work of historians and others in the ‘soft sciences’, where best practice requires an understanding of the limited reliability of different sorts of data, and the choice of the safest position within a virtual cocked hat. And just as it may be unwise to rely totally on a black box for navigation, so perhaps ‘fake news’ tells us something about the consequences of replacing soft scientific procedures with a confident acceptance of questionable data.

Nicholas Tracy
Fredericton, New Brunswick

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