How does GPS satellite navigation work? - Explain that Stuff Tweet by Chris Woodford . Last updated: November 13, 2016. Let's Get Lost is the title of a 1940s jazz song, famously recorded by singer and trumpeter Chet Baker. Back then, getting lost was not just a romantic idea but still a realistic one. Today, it's almost impossible to get lost, no matter how hard you try. Whether you're haring down the freeway or scrabbling up Mount Everest, you're always in sight of satellites spinning through space that can tell you exactly where you are. Walking round with a smartphone in your pocket, you'll have ready access to a GPS (Global Positioning System) receiver that can pinpoint your position, on a good day, to just a few meters. Take a wrong turn in your car, and a determined voice—also powered by GPS—will insist you "Take the next left," "Turn right," or "Go straight ahead" until you're confidently back on track. Even riding on a bus or train, it's barely possible to get off in the wrong place.

Handy display boards scroll the name of the stop you want long before you need to rise from your seat. Apart from helping us reach our destination, satellite navigation can do all kinds of other things, from tracking parcels and growing crops to finding lost children and guiding the blind. But how exactly does it work? Let's take a closer look! Photo: Getting lost is a thing of the past thanks to mobile devices like this with built-in GPS receivers and mapping apps. What is satellite navigation? Satellite navigation ("satnav") means using a portable radio receiver to pick up speed-of-light signals from orbiting satellites (sometimes technically referred to as space vehicles or SVs) so you can figure out your position, speed, and local time. It's generally much more accurate than other forms of navigation, which have to contend with pesky problems like accurate timekeeping and bad weather. Because it's a broadcast system based on radio signals that reach all parts of our planet, any number of people can use it at once, anywhere they happen to be. The best-known satnav system, the Navstar Global Positioning System (GPS), uses about 24 active satellites (including backups).

Day and night, 365 days a year, they whiz round Earth once every 12 hours on orbital planes inclined at 55 degrees to the equator. Wherever you are, you're usually in sight of at least half a dozen of them, but you need signals from only three or four to determine your position to an accuracy of just a few meters . GPS was kick-started by the US military in 1973 and its satellites are designed to last about 7.5 years, but the latest generation typically survive about 10–12 years. In total, around 60 Navstar satellites have been launched altogether, in several separate groups called blocks, though many of them have now retired; at the time of writing, the last Navstar launch was satellite IIF-9 on March 25, 2015. Photo: A NAVSTAR GPS satellite pictured during construction on Earth in 1981. You can get an idea how big the satellite is from the engineer pictured some distance beneath it. Picture courtesy of US Department of Defense.

GPS has three major components, technically known as "segments": there's one part in space, one part on the ground, and one part in your pocket. The 24 satellites form what's known as the "space segment" of GPS, but the system also relies on an intricate ground-control network of antennas , monitors, and control stations (the "control segment"), centered on a Master Control Station (MCS) at Shriever Air Force Base in Colorado, USA (with a backup at Vandenberg Air Force Base in California). Apart from the space and control segments, the other essential part of satellite navigation is the "user segment"—an electronic receiver you hold in your hand or carry in your vehicle. Triangulation Finding your position using satellite signals is a hi-tech version of an age-old navigator's trick that goes by the name triangulation. Suppose you're walking through the woods, on completely flat ground, but you don't know where you are. If you can see a landmark through the trees (maybe a distant hill), and you can guess how far away it is, you can look at a map and figure out that you must be somewhere on a circle whose radius (distance from the hill) is the distance you've guessed.

One landmark alone can't narrow your position any more than this. But what if you suddenly see a second landmark in another direction. Now you can repeat the process: you must be a certain distance from that object too, somewhere on a second circle. Put these two bits of information together and you know you must be somewhere where the two circles meet—one of either two places on the ground. With a third landmark, you can narrow your position to a single point. And that's the essence of simple triangulation (you'll find a longer introduction at Compass Dude ). Triangulation works with line-of-sight and a bit of guesswork, with a compass and a map, and with fancier methods like radio signals, and radar . And it also works, in a more sophisticated way, using space satellites. Photo: Ferdinand Magellan (1480–1521) sailed the globe with great skill and ingenuity, proving that the "flat Earth" was, in fact, more or less spherical. It's tempting to imagine how much easier Magellan's life would have been with satellite navigation, but that gets the logic of things the wrong way round.

Without Magellan's insight, we wouldn't have satellite navigation technology at all: to build it and get it working, we had to know that we lived on a round Earth to begin with! Public domain engraving courtesy of US Library of Congress . Trilateration With satellite navigation, your navigational "landmarks" are space satellites whizzing through the sky above your head. Because they're about 20,000km (12,600 miles) away, well beyond Earth's atmosphere, and because they're constantly moving (not stationary, like Earth-bound landmarks), finding your position from them is a bit more tricky. If you pick up a signal from one satellite and you know it's 20,000km away, you must be somewhere on a sphere (not a circle) of radius 20,000km, centered on that satellite. With two signals, from two different satellites, you must be somewhere where two spheres meet (somewhere in a circle of overlap). Three signals puts you at one of two points on that circle—and that's usually enough to figure out where you are, because one of the points might be up in the air or in the middle of the ocean.

But with four signals, you know your position precisely. Finding your location this way is called trilateration. How GPS works Photo: An artist's impression of the 24 NAVSTAR satellites in orbit around Earth. Picture courtesy of US Department of Defense. Satellite navigation systems all work in broadly the same way. There are three parts: the network of satellites, a control station somewhere on Earth that manages the satellites, and the receiving device you carry with you. Each satellite is constantly beaming out a radio-wave signal toward Earth. The receiver "listens out" for these signals and, if it can pick up signals from three or four different satellites, it can figure out your precise location (including your altitude). How does that work? The satellites stay in known positions and the signals travel at the speed of light. Each signal includes information about the satellite it came from and a time-stamp that says when it left the satellite. Since the signals are radio waves, they must travel at the speed of light. By noting when each signal arrives, the receiver can figure out how long it took to travel and how far it has come—in other words, how far it is from the sending satellite.

With three or four signals, the receiver can figure out exactly where it is on Earth. Where in the world are you? If your satellite receiver picks up a signal from the yellow satellite, you must be somewhere on the yellow sphere. If you're also picking up signals from the blue and red satellites, you must be at the black dot where the signals from the three satellites meet. You need a signal from a minimum of three satellites to fix your position this way (and four satellites if you want to find your altitude as well). Since there are many more GPS satellites, there's more chance you'll be able to locate yourself wherever on Earth you happen to be. How do satnavs calculate distance from time? Suppose you're carrying a GPS-enabled cellphone or satnav in your car. How does it know the exact distance to the three or four satellites it uses to compute your position? Every satellite constantly beams out signals that are, in effect, time-stamped records of its position at that time. Since they're carried by radio waves, the signals must be traveling at the speed of light (300,000km or 186,000 miles per second).

Theoretically, then, if a receiver picks up the signals some time later, and has a clock of its own, it knows how long the signals have taken to get from the satellite, and how far they've traveled (because distance = speed × time). That sounds like a nice, simple solution, but it introduces two further problems. First, how long does the signal take to travel? Haven't we just swapped one problem for another (time for distance)? The solution to this involves a hi-tech version of "synchronizing watches": each satellite carries four extremely precise atomic clocks (two cesium and two rubidium, typically accurate to something like one second in 100,000 years), while the receivers (which have less accurate clocks of their own) receive their signals and compensate for the time it takes for them to travel down from space. That means each receiver can figure out how long each signal has taken to reach it and therefore how far it's traveled. Second, although radio waves do indeed travel at the speed of light, they only do so in a vacuum (in completely empty space).

Radio signals beaming down to us from space satellites aren't traveling through empty space but through Earth's atmosphere, including the ionosphere (the upper region of Earth's atmosphere, containing charged particles, which help radio waves to travel) and the troposphere (the turbulent, uncharged region of the atmosphere, where weather happens, which extends about 50km or 30 miles above Earth's surface). The ionosphere and troposphere distort and delay satellite signals in quite complex ways, for quite different reasons that we won't go into here, and GPS receivers have to compensate to ensure they can make accurate measurements of distance. Are military and civilian GPS any different? Photo: Satellite-guided missiles and drones use the military-grade PPS version of GPS, which is theoretically more accurate than civilian GPS. Photo by Nicholas Messina courtesy of US Navy . GPS was originally conceived as a military invention that would give US forces an advantage over other nations, but its inventors soon realized the system would be just as useful to civilians. The only trouble was, if civilians (or rival forces) could pick up the same signals, where would that leave their military advantage?

For that reason, they developed two different "flavors" of GPS: a highly accurate military-grade, known as Precise Positioning Service (PPS), and a somewhat degraded civilian version called Standard Positioning Service (SPS). While PPS-enabled receivers could originally locate things to an accuracy of about 22m meters (72ft), SPS receivers were deliberately made about five times less accurate (to within the length of a football field, or about 100m) using a tweak called Selective Availability (SA). That was switched off by order of US President Bill Clinton in May 2000, greatly improving accuracy for civilian users, which is largely why GPS has taken off so readily ever since. Even civilian SPS receivers are now officially accurate to within "13 meters (95 percent) horizontally and 22 meters (95 percent) vertically", though a variety of different errors (caused by the atmosphere, obstructions blocking line of sight to satellites, signal reflections, atmospheric delays, and so on) can compound to make them very much less accurate at times. Theoretically, military and civilian GPS could be as accurate as one another if we didn't have to worry about them traveling through Earth's atmosphere.

According to the official website GPS.gov : "The accuracy of the GPS signal in space is actually the same for both the civilian GPS service (SPS) and the military GPS service (PPS)." In practice, while SPS signals are broadcast using only one frequency, PPS uses two. Comparing the two frequencies allows military grade GPS receivers to calculate precise corrections for radio delays and distortions caused by transmission through the atmosphere, and that still gives military GPS an edge over civilian systems. In time, civilian GPS will become increasingly accurate, especially as more satellites (and more different satellite systems) are added, but it's likely that military systems will always have an advantage, for one reason or another. GPS satellite signals Navstar satellites constantly broadcast the two different flavors of GPS, PPS and SPS, on two different radio frequencies (carrier waves) known as L1 (1575.42MHz) and L2 (1227.6MHz).

L1 carries the civilian SPS code signal (also known as the C/A code or Coarse Acquisition code), which is relatively short and broadcast about 1000 times a second, and what's known as the navigation data message, which includes the date and time, satellite orbit details, and other essential data. L2 carries the military PPS code, also known as P-code (Precision code), which is very long and precise and takes an entire week to transmit. It's encrypted to form what's known as the Y-code, partly so that only authorized users can access it, and partly (because encryption is a form of signing things to confirm they're authentic) to help prevent things like "spoofing" (where third parties broadcast fake, disruptive signals purporting to be from GPS satellites). Military-grade GPS receivers pick up both frequencies, and compare them to correct for the effects of the ionosphere. Civilian receivers pick up only one frequency and have to use mathematical models to correct for the ionosphere instead. Applications of satellite navigation Most of us use satellite navigation for driving to places we've never been before—but that's a relatively trivial application. Once you can pinpoint your precise position on Earth, much more interesting things become possible.

Roll time forward a few decades to the point where all cars have onboard satnav and can drive themselves automatically. Theoretically, if a car knows where it is at all times, and can transmit that information to some sort of centralized monitoring system, we could solve problems like urban congestion, finding parking places, and even auto theft at a stroke. If every car knows its location, and knows where nearby cars are too, highway driving could become both faster and safer; it will no longer rely on the vigilance of error-prone human drivers, too easily confused by tiredness and bad weather, so cars will be able to travel at much higher densities. The same goes for airplanes , where GPS is finally set to become an integral part of air traffic control—gradually reducing our historic overdependence on radar—over the next decade. Photo: Many tractors, combine harvesters, and crop dusters are now equipped with GPS. And it's not just cars and planes that will benefit from pinpoint precision. For emergency services and search and rescue workers, navigating to remote, sometimes uncharted locations, in a hurry, makes all the difference between life and death.

Farmers have been using GPS systems in tractors , combines , and crop-dusters to map, plant, manage, and harvest their crops with efficiency and precision. According to an industry body called the GPS Alliance, high-precision satellite navigation boosted US crop yields by almost $20 billion from 2007 to 2010 and is now used in 95 percent of crop dusting. Meanwhile, farm animals, pets, and rare wildlife are easier than ever to track using GPS-enabled collars and backpacks. Blind people, traditionally guided by seeing-eye dogs or the elbows of friends and family, can finally gain true independence equipped with talking handheld GPS systems, such as Trekker Breeze, that can announce street names or read spoken directions from A to B. Needless to say, a system conceived by the military still enjoys many military applications, from guiding so-called "smart bombs" to their targets with pinpoint accuracy to helping troops navigate through unfamiliar terrain. GPS is as standard a part of modern military equipment as maps and compasses were 100 years ago.

Rival satellite navigation systems In the United States, GPS is universally used as a synonym for any and every kind of satellite navigation; in other countries, such as the UK, "satnav" is a more familiar generic term. In fact, GPS is only one of several global satnav systems. The Soviet Union launched a rival system called GLONASS in 1982 (also using 24 satellites) and Russia continues to operate it today. Europe has been slowly building its own, more accurate 30-satellite system called Galileo, which is expected to be completed around 2020, and China is developing a global system known as Compass. The preferred umbrella term for world-spanning satnav systems is GNSS (Global Navigation Satellite Systems). Apart from the four big global systems, there are also a few smaller regional rivals, including China's BeiDou and India's IRNSS. Although a given satellite receiver is typically designed to use only one of the global systems, there's no reason why it can't use signals from two or more at once.

Theoretically, combining signals from GPS, GLONASS, and Galileo could give satnav devices something like a 10-fold increase in precision, especially in urban areas where tall buildings can block or distort signals, reducing the accuracy of any one system used alone. Using multiple systems also promises to make satellite navigation much faster: if more satellites are "in view," the so-called Time-to-First-Fix (TTFF) —the initial delay before your satnav locks onto satellites, downloads the data it needs, and is ready to start calculating your position—is reduced. Since TTFF typically varies from about 30 seconds to several minutes, it makes a big difference to casual GPS users (and is one of the first features people compare when they look at buying a new satnav receiver). Challenges and issues Knowing the absolute position of anything, anytime, anywhere brings obvious benefits in a globalized world that relies on swift, safe, and reliable transportation. But it raises issues too. If civilian transportation systems are designed to rely on satellite systems provided by the US or Russian military, doesn't that make us too vulnerable to the sudden twists of international politics, especially in times of war?

Although the US military no longer routinely degrades the quality of GPS signals, and announced in September 2007 that it would be removing Selective Availability altogether from future versions of GPS satellites, currently it can still nobble the system anytime it pleases. Could a future world of driverless cars, hyper-efficient parcel shipping, and automated air-traffic control be plunged into chaos purely at the whim of the superpowers? The European Galileo project is entirely a civilian system, which should eliminate possible military interference in time. But for the moment, it remains a concern. Fast-disappearing privacy is the flipside of the same coin. If your car and your cellphone are both equipped with satnav, and you're always using one or the other (or both), your movements can be tracked at all times. That raises obvious privacy issues, especially in repressive states. But every new technology brings its pros and cons, from internal combustion engines to submachine guns, and nuclear power plants to antibiotics. Progress involves making a tradeoff between benefits and costs, in the hope of doing things better than we ever could before.

Satellite navigation is no different, swapping safe and unreliable navigation for efficient and effective transportation, albeit at a cost in privacy and (for the time being) continued dependence on military infrastructure. GPS.gov : The official US Government site all about GPS and its applications. GPS Innovation Alliance : A trade coalition furthering greater use and new applications of GPS. USNO GPS Timing Operations : A variety of useful GPS data from the US Naval Observatory. Articles Protecting GPS From Spoofers Is Critical to the Future of Navigation by Mark L. Psiaki and Todd E. Humphreys. IEEE Spectrum, July 29, 2016. It's difficult but not impossible to spoof GPS signals, potentially sending ships and boats on course to disaster. What technical methods are there to protect against spoofers? What Stand-Alone GPS Devices Do That Smartphones Can't by Eric A. Taub. The New York Times, July 15, 2015. There are still good reasons to own a standalone GPS device, although now smartphones have bigger screens the gap between the two kinds of devices is closing fast.

Russian Global Navigation System, GLONASS, Falling Short by James Oberg, IEEE Spectrum, February 1, 2008. Can Russia's alternative ever hope to compete with GPS? End of Flight Delays? FAA's GPS Fix Could Bust Sky Gridlock by Barbara S. Peterson, Popular Mechanics, July 19, 2007. An introduction to the use of GPS in air traffic control. Books The Global Positioning System: A Shared National Asset by Aeronautics and Space Engineering Board, National Research Council. National Academies Press, 1995. A technical report evaluating the success of GPS and making recommendations for its future development as a joint civilian and military system. Technical references GPS Performance Standards : The official SPS and PPS specifications, downloadable in PDF format. GPS Factsheet : Technical details about Navstar from the US Air Force. Patents Garmin | United States | Home United States Learn More Action Cameras VIRB® action cameras capture it all, with wide-angle optics and advanced microphone technology. Built-in sensors record speed, altitude, G-force, GPS position and more. Automotive Automotive Drive confidently with personal navigation devices designed for cars, trucks, motorcycles and RVs.

Also shop dash cams, backup cameras and in-vehicle camera monitors for even more awareness when you’re behind the wheel. Sports & Recreation Sports & Recreation Track activity, golf, swim, hike, cycle, run, even track and train dogs with innovative products made to keep up with your lifestyle. Best Sat Nav 2016 Round-up Home / Product Round-ups / GPS & Sat Nav / Best Sat Nav 2016 Round-up Best Sat Nav 2016 Round-up by Joe Roberts Read Comments Looking for a new sat-nav to make your journeys as pain-free as possible? Look no further. We've rounded up the top sat-navs available right now. Whether you're trying to decide between TomTom or Garmin or considering whether it's worth shelling out for a top-end device, you're bound to find something here. Although most people will use their smartphone for navigation these days, the standalone sat nav is still one of the most reliable ways of getting from A to B. Many still prefer having maps pre-installed on their sat-navs, rather than relying on their smartphone's data connection to ensure map data can be downloaded on the fly.

What's more, dedicated sat-navs will usually feature shine-free screens and you don't have to worry about interruptions such as phone calls or notifications. When it comes to buying a standalone sat-nav then, options range from around £50 to around £300. These days, the industry is dominated by TomTom and Garmin, so there's not as much choice as there once was. But there's still some great devices available, all of which you can find in our round-up. Before buying a new sat-nav, however, there are several factors to consider. You'll want to look for something that's going to get you to your destination as easily as possible, updating you on traffic changes and alternative routes. This week's best sat-nav deals TomTom Go Start 50 at Amazon.co.uk | Was £139 | Now £84 Maps Firstly you have to determine whether you'll be using the device abroad or just in your own country. Most sat-navs will come with European maps, but only some will include world maps, and not all will provide you with lifetime updates, meaning you'll have to pay for map pack updates in the future.

Most models will come with free updates, but be careful when buying older models, as you may find yourself having to shell out in the future. Traffic Secondly, you should consider whether you want your sat-nav to come with traffic updates. These days, most sat-navs will feature some sort of traffic service, alerting you to delays and traffic jams. But it's still worth checking, if you want to ensure you don't get caught out, that the model you're thinking of buying comes with a traffic service and whether that service requires you to pay after a certain time. Some devices will come with built-in traffic updates while others will require you to pair your smartphone in order to use its data connection for traffic information. Many sat-navs will also feature speed camera warnings. Again, it's worth checking whether this feature comes as standard or whether it's a paid extra. Size You should also consider how big a screen you will need. If you want to limit how much the device obstructs your view, there's a range of sat-navs with 4-inch screens available. If you don't mind something a little bigger, you can pick up devices featuring screens of up to 7 inches.

Bearing in mind, you average smartphone will measure anywhere from 4 to 6-inches, it's worth considering how big you want your dedicated device to be. There's also the resolution. Many entry-level sat-navs will feature a 480 x 272 display, which is adequate for displaying navigation directions and maps, but if you want to use the device to get information on local areas of interest and so on, you may want to consider a model with a slightly higher resolution screen. Aside from these main considerations, there are other extras to look out for such as voice control and Bluetooth connectivity which will allow you to use the sat nav for hands-free calling. With all this in mind, take a look at our sat-nav round-up and see which model is right for you. September 20, 2013, 1:39 pm So where does it tell me which is the best to buy? Elena September 23, 2013, 9:36 am Hello there, i am struggling to buy a good sat nav and after a loong reasearch i ended up to this one.

I went to the store to buy it and i tried there to put in some postcodes. I put in my home postcode but it came up different address and my address was also there with wrong postcode. When i tried to put in house number it wouldn't accept it and was telling me that there is no such a hous number on thar road!! Anyone has any idea what is this about? Thanks Evan September 23, 2013, 11:30 am Hi Elena I have a similar issue with my house and it has to do with roads changing without central maps being updated. It will take a while but maps should catch up with the new postcode. In the meantime I have found an address and postcode that actually shows my house's location and I provide that to cab drivers or people coming to visit so they don;t get lost. Darryl October 27, 2013, 1:18 am I ordered the garmin hud unit from Amazon. I got it last Thursday. I've been testing it for the last few days. I like it. I am not as distracted as in the past, when I had to look down at my phone while driving.

I had this thought of me maybe running into the back of a stopped 18 wheeler, perish the idea. If this unit can prevent something like that from happening it is a good investment. Freddie Headey December 5, 2013, 8:48 pm It would be good if you had a link to a chart showing features/price/need for smartphone. Also some reviews of the £60 -£120 one I think I've seen from Halfords/Currys & info on what is missing on them. Thanks lesleysivo December 7, 2013, 8:27 pm I am looking at both TomTom via 130 and Garmin Nuvi 52LM as both on special at Argos for 99.99 at the mo. Use in Europe aswell as Uk but not sure which one is best...please can anyone advise? cheers lesleysivo December 7, 2013, 8:29 pm have the same problem...which is best for general use? Argos specials for UK and Europe at 99.99...Garmin or TomTom???? can anyone help??

cheers Garmin by all measures December 21, 2013, 4:45 am I compared a newly bought Tom Tom device to a Garmin that is at least 6 years old and although the Garmin had some missing roads, the Garmin was better in every fashion without a doubt. The Tom-Tom had poor instructions and confusing directions during driving which many times giving incorrect locations and changing directions during a drive without notification. Dave December 29, 2013, 11:48 am Hi, Can anyone help My wife and I are setting of to drive to Thailand from the UK in March 2014 and I am looking for a sat nav to use on the way as anybody got any ideas Dave Guest February 28, 2014, 10:03 am I bought my garmin also about 6 years ago, and had the same problems you are attributing to tomtom! Alex July 9, 2014, 9:08 am Driving from the UK to Thailand ?! O.o Is it worth of being visited ?

Joe August 25, 2014, 5:58 pm Whatever you do, be sure to update the maps database just before you leave. These devices are always 2 years behind in road changes. Joe F Terry Pearce September 24, 2014, 3:28 pm I just want a satnav that turns down my stereo so that I can hear the spoken instructions. I have a Tomtom Start 25 but I would be happy to trade up. Egzie November 15, 2014, 12:39 am I've just returned my via 130 to Argos as it said it had no maps and would'nt update after 10 months. Days scanning tomtom website and as a former computer lecturer I was stumped!?! 4 year old battery and tech! staysafe November 17, 2014, 7:17 pm Looking for a sat nav with low bridges, narrow roads, weight restrictions etc. Been looking at NozaTec 7 inch truck.

Anyone know anything about this make as I have not heard of them before and they seem to be so much cheaper PETE December 10, 2014, 12:05 pm I looked at Noza Tec 7inch I would like to hear from anyone with knowledge of them phil February 26, 2015, 8:05 am hi how did it go driving to thailand would love to do it myself Saji October 12, 2015, 10:08 am Received an offer from TOMTOM in email. 18 months LIVE SERVICES for the price of 12 months. Purchased on 30 September, 2015. Downloaded and ended up washing up my device. Lost all the data. Contacted customer services on 01 October and today it is 12 October. Still waiting for any solution or refund. My advice to people, TOMTOM has VERY POOR CUSTOMER SERVICE, NO PRODUCT SUPPORT, BEST AVOID AND STAY AWAY. THEY ARE QUICK TO TAKE MONEY BUT TOO LAZY TO DELIVER.

Jamesehw December 15, 2015, 11:54 am AVOID TOMTOM. All the physical bits feel robust and well made. The first time I tried to update my map the device erased the existing map and spent many hours trying to download the updated map. In the end I called tomtom support, who talked me through the basics and made me spend many more hours trying to download the map. I have spent a week now with a useless tomtom. I have spent hours on the phone to their support jumping through their hoops, and days and nights trying to download the map. I have repeatedly asked where I can send it to have it replaced but support always insist "don't worry, by the end of today it will be working fine". On day 8, I have been told that the current issue is that the newer map is slightly bigger than the old erased map and will not fit on the device any more. I need to add a memory card. I have a spare card to hand so, I am now waiting for my latest download attempt. 24% downloaded, 2hr 33mins to go....

dogdays1 May 7, 2016, 9:28 pm I have both units. The downfall of Tomtom is their safety camera database and the My Drive connection for upgrades. Their safety camera database only seems to carry fixed cameras in the UK, no mobile unit locations.The Garmin Nuvi allows me to download third party databases, which Tomtom will not, and also gives loud spoken camera zone warnings. Tomtom customer service is awful. The latest upgrades have nasty habit of destroying your units abilities and Tomtom just don't give a damn. I am now after 10 years with various Tomtom units a Garmin fan. Mark Packham May 16, 2016, 10:19 am I have a 2 year old TomTom XXL classic with 2Gb of memory. It will not hold all of Western Europe so I have to use MapZones. Beware, with difficulty you may be able to load 2 zones into your satnav memory, but you are not allowed to plan a route that crosses over from one zone to another, this has to be done on a computer. Do you want to carry around a laptop on holiday?

For instance you cannot plan a route from the UK to anywhere in Germany, the UK is in the Western Zone, Germany in the Northern Zone. I am about to go on a touring holiday based in southern Germany in the foothills of The Alps, sadly Switzerland, Austria and Italy are in the southern zone so full route planning will not be possible while I'm there. Robert Kaye January 1, 2017, 4:16 am The noza tec sat navs are ok they do the job but they are a nightmare to update. Tom Tom, GPS and Sat Nav | Reviews | TechRadar Tom Tom, GPS and Sat Nav Tech deals, prizes and latest news Get the best tech deals, reviews, product advice, competitions, unmissable tech news and more! No spam, we promise. You can unsubscribe at any time and we'll never share your details without your permission. Most Popular Best GPS Reviews – Consumer Reports GPS selector What's behind our GPS Ratings? Experts at our National Testing and Research Center tested 14 models in GPS to see which ones perform best.

We look for: Overall score This score mainly reflects how easy a navigation system is to use, combined with factors such as information given, portability, and routing options. The displayed score is out of a total of 100 points. Screen size The diagonal length of the display screen measured in inches and rounded to the nearest tenth on an inch. Ease of use Ease of use score is based on an assessment of the physical interface, touch-screen control, programming logic, and readability. Testing considers such things as whether the database allows dynamic searching for addresses, if unlikely letters are grayed out, ease of entering into navigation menus upon start-up, ease of finding points of interest, and ease of adjusting common functions like volume, brightness, and map zoom setting. Routing options Our routing evaluation looks at the choices for fine-tuning a route and calculation time. Specifically, we factor multi-destination routing, avoidance of toll roads, biking routes, walking routes, RV/truck use, and availability of foreign map databases. In addition, we measure system response time when operating data-entry menus, such as POI searching. Driving guidance Based on the on-screen and audible information given to the user during navigation.

Includes type and font size of on-screen information, ability to speak proper street names, languages supported, and amount of audible information given including descriptions of the next maneuver, including lane assist and reality view. Mount design Considers how the mount is engineered, factoring size, security, and ease of installation. Display quality Display quality reflects image clarity, color accuracy, and contrast as judged by panelists who viewed text and photos, and on lab measurements. Traffic interface Rates the presentation of the traffic information and the ability to put the data into use. Rating factors include color coding for traffic severity, depth of information, estimated time for delay, and tools for rerouting around congestion. However, we do not rate the accuracy or timeliness of the traffic information itself. Connect Share your reviews and provide valuable feedback to other members and our testers. Follow Consumer Reports Recommended GPS Recommended GPS are standout choices with high scores. They include CR Best Buys, which offer exceptional value. When narrowing your choices, weigh features, price, and attributes that matter to you. GPS Unit Buying Guide | eBay GPS Unit Buying Guide Share March 3, 2016 GPS units have been revolutionizing travel since the inception of the Global Positioning System in the 1970s.

Armed with a single device, users can access the Global Positioning System to determine their precise location anywhere in the world, 24 hours a day. A GPS device can also provide the user with turn-by-turn street-level directions, real-time traffic conditions, and precise speed when in a motor vehicle, on a bike, or on foot. In short, accessing the GPS network allows the user to replace paper maps and forego handwritten directions in favor of a 24-hour, on-call navigation system. Because GPS units vary greatly in size and quality, it is important to understand the types and uses available. Those looking to buy a GPS unit should understand the history and purpose of the GPS, the general functions, applications, and benefits of GPS units, the ways in which they intend to use the desired device, and the different types of GPS units available to consumers. Overview of GPS Originally called NAVSTAR (Navigation System with Timing And Ranging), the GPS was officially launched in 1978 by the U.S. Department of Defense. It was originally a satellite system designed for military use that drew on the existing technology of the U.S. Air Force and U.S.

Navy, and it was based on the early work and development of M.I.T. researchers in the 1950s. These satellites were used extensively by the U.S. military throughout the 1970s for surveying, tracking, and navigation, and they were made available for public use in the 1980s. Throughout the next two decades the functionality and accessibility was continuously improved to the point where the average individual can use the technology intuitively without much learning curve. The most common types of GPS units today are small handheld devices, including those in smartphones and models designed for the car, but there are many other types as well. Benefits of Using GPS Units Use of a GPS device provides the consumer with a host of benefits over traditional maps. When shopping for a device, one must be certain that it provides the basic benefits described below. Map Coverage GPS units provide detailed maps for entire countries, and some are programmed with data for all of a particular continent. Depending on the intended use of the GPS device, actual map data may vary. For example, all GPS units designed for the car provide users with very similar street maps.

Car units typically also feature a three-dimensional bird's eye view that enables the user to visualize the landscape as if they were viewing it above street level. Handheld devices designed for fishing or boating , on the other hand, are obviously loaded with maps that help the user visualize other points of interest, such as lakes and rivers. Before purchasing a GPS unit, the consumer must pinpoint where they will be likely to use the device most often so they can target a device with the right type of map coverage. Travel Directions The most basic and widely used function of the GPS unit is the turn-by-turn navigation it can provide. GPS units provide accurate directions between any two points and can constantly monitor the user's position and progress. Also, GPS units provide the user with feedback on the route they are actually taking. The directions are often recalculated if the user makes a wrong turn or decides to take a different route, so the user can never get lost. GPS units designed to be mounted in the car , such as the Magellan Roadmate 1700 , usually provide both visual and audio directions so the user does not have to divert their attention from the road if they are in motion.

One indirect bonus of a GPS unit is increased fuel economy, as the user can save time and money by following a direct route each time they depart for a new destination. Destination Stops Most GPS units help the user find certain points of interest, such as gas stations, coffee shops, restaurants, and hotels, along their way to a certain destination. Automotive GPS units have millions of stops programmed into their maps, and these can be a great benefit to the user who is traveling a great distance or driving in an unfamiliar town or city. Most units allow the user to search for specific points of interest by name or category, browse for those near their current location, or even look up stops in a different region for future reference. Avoiding Traffic Some GPS units are equipped with built-in traffic monitors that automatically inform the user of potential jams on the intended route. This is another feature than can allow the user to save time and money, and at the very least, the headache of having to sit in long lines on the way to a destination. Safety Regardless of the intended use of the GPS device, the ability to avoid getting lost and encountering a potentially dangerous situation is a definite plus. Rescue crews, firefighters, and tour guides use GPS units every day.

The ability to provide emergency workers with a precise location in the event of an emergency or accident could be a life-saving feature. Types of GPS Units Buyers should consider their personal needs and budget before buying a GPS unit. There are many different types of GPS units available, including portable units, built-in factory systems, cell phone navigation subscriptions, and GPS smartphones. Portable Units Portable GPS units can range anywhere from about $80 to $400, and they have several key advantages over other types of devices. They are relatively inexpensive (compared to built-in systems), they can be transferred between vehicles, and their small size makes them easy to pack and store in luggage if going on a trip. Also, updating maps and traffic information is relatively inexpensive and easy. Drawbacks of portable units include the potential for the device to be lost or stolen and the small screen size, which can be difficult to read. If using a portable device in the car, it is recommended that it be stowed away out of sight when the car is locked up so it does not present a target for thieves.

Built-In Systems Built - in ( or in - dash ) GPS systems are available on most new car models as an optional feature, and some can be purchased as part of a premium stereo system. They typically add at least $1,000 to the purchase price of the car and can cost much more than that. However, they have large, clear screens, easy-to-use controls, and they often respond to voice commands, which is a huge plus when operating motor vehicle. Obviously, these units cannot be transferred between vehicles, but they can certainly be a worthwhile investment if the buyer uses one vehicle exclusively. Cell Phone Navigation Subscriptions Some of the most popular cell phone carriers offer GPS navigation services by subscription. This typically costs the buyer an additional $10 per month, and some plans can be purchased for a per-diem fee as well. The key advantage with this system is the ability to use one portable device for both calling and navigating. However, the screen size of most cell phones are very small, and operating the map with keyboard controls can be cumbersome while driving. GPS Smartphones Different from cell phone navigation subscriptions, smartphones allow the user to purchase an app and use the downloaded software for navigation. This application turns the phone into a portable GPS unit.

If GPS is a strong consideration when buying a smartphone, the buyer should look for a phone that has a large, colorful display and touchscreen controls for greater ease of use. How to Choose the Right GPS Unit Before deciding on a GPS unit, buyers should think about their main reasons for purchasing the device, their typical driving conditions (if planning on using the unit in the car), and the features that would be most helpful on a regular basis. Type of Driving If most of the driving is done in one neighborhood or along familiar routes, then a high-tech, expensive device may not be the most cost effective option. However, if there is usually heavy traffic or congestion on the route to or from work, a GPS device can help navigate around these problems when they occur. Frequency and Type of Use Buyers in the market for a new vehicle may find that most new cars can be purchased with GPS units built into the system. The difference between this and hand-held or mounted GPS units is obviously portability. If the buyer plans to use the GPS system exclusively when driving, then an additional GPS unit is not a necessary purchase.

However, many new GPS units can be used both in the vehicle and as a hand-held device, so those who do a lot of walking or hiking in unfamiliar territory should invest in a portable unit. Since newer cell phones are also GPS compatible, the buyer should compare the features of their cell phone navigation with the unit they are planning to buy. Portable GPS units typically provide more detailed map coverage and are easier to use than cell phone navigation, but for each buyer it is a matter of balancing cost with need. Key GPS Features GPS units can come equipped with a host of features, including MP 3 players , Bluetooth compatibility , and photo viewers. Those looking to use their GPS system for fairly specific uses, for example, runners who want to use it to determine their heart rate , should make sure the unit they are buying provides that particular feature. Those who are mainly concerned with navigation should look for a unit with an appropriate screen size, spoken street names, real-time traffic reports, and predictive data entry. Screen Size The average size of a portable GPS unit is 4.3 inches , measured diagonally.

This is an acceptable size for units that will be used in the car or on foot, as they provide enough room for a touchscreen keyboard to be operated without difficulty, and the screen is large enough for someone to analyze the map while driving. Those looking for a larger screen should consider the way in which they will be using the device. A 7 inch screen , for example, may be too large to mount on the windshield of a compact car and therefore impractical for some users. Spoken Street Names GPS units that speak to the user and can identify specific street names are incredibly helpful. In unfamiliar areas with confusing intersections, the ability to simply listen to the GPS and identify a street or highway by name is crucial. This is a must-have feature for those who are looking to use the GPS in the car. Many cell phone plans and smartphone apps do not have this feature, so it is something to look out for in a stand-alone unit. Traffic Reports and Detour Features GPS units that supply traffic information allow the user to detect a problem ahead of time and potentially avoid it altogether. When looking to buy a GPS unit, pay attention to the type of traffic alerts that are provided.

Some units automatically alert the user to traffic, while others require the user to search for any potential delays manually. Also, some GPS packages, especially smartphone-based systems and apps, may charge extra for this particular service. Predictive Data Entry Almost all portable GPS models are equipped with predictive data entry. This is an extremely handy feature that will search the database for cities, street names, or points of interest that begin with the letters the user has typed. For example, if the user is looking for a street name that begins with the letters Bro-, it will automatically fill in Broadway and calculate the distance to this particular street. It is especially helpful when the user cannot remember the entire name of a destination. Using eBay to Purchase GPS Units The various types and prices of GPS units can make purchasing one seem like an intimidating process. Most electronics stores and big box department stores carry GPS units, so these may be appropriate places to shop. However, none of these stores can match the enormous collection of new and used GPS units that eBay provides. Only with eBay can the consumer sift through thousands of different types of GPS units without ever leaving the comfort of home. Sort Listings and Find the Right Item When visiting the eBay home page, locate the Search bar near the top of the screen.

Use this space to type in the desired type of GPS unit you want. If you type in the words "GPS unit" in a general search, thousands of results will be provided. On the left-hand side of the screen is a taskbar that allows you to narrow your search by type of GPS, brand, screen size, condition, and price among other categories. After finding the desired GPS unit, such as the Garmin Nuvi 285 W , click on the blue hyperlinked text next to the item. This brings you to a page where you can purchase the item. Know the Seller A buyer should get to know the seller before making a purchase. One way to do this is to see if other customers have left positive feedback on the seller's profile. When you have zeroed in on the desired product, take a look at the seller's ratings and feedback on the right hand side of the page. You can find out if the seller has a solid track record and whether or not he or she has established themselves as someone who ships items out quickly. Conclusion GPS units are in use everywhere.

Those who frequently venture into new regions, have difficulty reading paper maps, or are just looking to simplify their travel experience can use GPS units to get from point A to point B. Thankfully, the widespread use of these navigational tools has brought the price of these handy devices down so they are affordable for the average consumer. Overall, the key to purchasing the right GPS unit lies in the knowledge of how the buyer will use it most frequently and the amount that the buyer is willing to spend on the device. Also, buyers should make sure that their cellular device or smartphone is not already suitable for their needs, as most of these devices are GPS compatible or even fully GPS ready upon purchase. If this is not the case, then exploring eBay to find the right GPS unit is a user-friendly way to acquire one of these helpful devices.

Question: In modern technology SatNavs use the GPS system. For what do the letters GPS stand?
Answer: GLOBAL POSITIONING SYSTEM