iPhone Confidential: GPS

| Just a Thought

There are those who believe that Apple's iPhone is based on technology that Steve Jobs singlehandedly wrested from aliens.

There are those who believe that the iPhone, given the right app, can churn butter, give its owners E.S.P., and make a delicious Western Omelet.

There are those who believe that if they were deposited in the middle of some bleak, barren nowhere all they would need is a ball of twine, a magnifying glass, a pocket knife, and an iPhone to survive.

I may be exaggerating, but only a bit. It's amazing how one device can engender such a following.

Apple has, with the help of the application development community, fostered the belief that the iPhone can pretty much do anything.

Are you lost? Check Google Maps on your iPhone. Famished? Give Urbanspoon a shake. Need to get your shoes repaired, get an oil changed, or get a vasectomy? Yellowpages on your trusty iPhone can point the way.

It's really become hard to know just what the phone that Steve built will or won't do, so I thought I'd start taking a real hard look at this device I've become so dependent on -- I mean REALLY look -- without the fanboy glasses, and see just what this device can do, will do, but more importantly, won't do.

This won't be an iPhone bitch session; what I want to do is examine the features of the iPhone as objectively as I can, maybe compare them to similar features on other smart phones. I'll even try to get comments to app developers and, it they choose to speak, Apple.

The point of this exercise is to lay bare the real device so that:
- Owners and potential owners know exactly what they are getting
- Point out areas that an app developer can fill
- Maybe even give Apple some feed back so they can make the iPhone better

Ok, the first topic: GPS

Here's the scenerio: From time to time I go out looking for stuff to photograph. I get up early in the morning, get in my car, point it in a general direction, and go until I find something that catches my eye.

Often I wind up in out-of-the-way places, on back roads that don't have names, or in towns so small the mayor, police department, trash collector, and only resident are all the same person.

In fact, on a recent Saturday I found myself on a swampy dirt (strike) mud road miles from anything that resembles civilization, in a wildlife management area along Florida's Indian River. I wasn't lost (I am a man after all), but the thought did cross my mind that if my small SUV got stuck I would not be able to tell anyone where to find me.

I imagined trying to live in the wild while waiting for someone to notice that I was missing. Roughing it, eating tree bark and grubs and drinking rain water. I'd fashion fishing tackle from palm fronds and a safety pin, find tubers and berries, and by the time my rescuers found me I will have created a four course meal complete with dessert and coffee (roasted acorns).

Then I noticed something in the water watching me as I drove by. I'm not sure what it was but I had no desire to find out and I wished I had been a boy scout when I was a kid.

I chastised myself for being too cheap to buy a nice GPS device, then I recalled that I own an iPhone and I have Google Maps AND MotionX GPS. I have everything I need to direct my rescue party to my exact location.

Well, not so fast.

The iPhone's GPS system is not what most think it is. GPS is an acronym for Global Positioning System, and that can mean any system that can be used to give a reasonably accurate location in real time. Most think that means the exclusive use of the system of global positioning satellites our taxpayer dollars have hoisted into orbit, and to an extent that's true, but the iPhone uses several types of GPSs to give you a location. Unfortunately, none of them are great in every situation.

First there are those satellites, which work pretty good if you can get a signal. Unfortunately, getting a good signal in any other car but a ragtop with the roof down is dicey at best. That isn't a problem, of course, if you're out walking about, but if you're in a car speeding down the highway then getting out is out of the question.

The second and less understood GPS that Apple employes is based on trigonometry. Triangulation pinpoints your location by forming a triangle between three or more cell phone towers or between you and two cell phone towers and calculating your location using the signal strength as vectors. This method can use either Wi-Fi or cellphone signals and can be used inside your car. That's because cellphone signals are stronger and most of the time you are reasonably close to at least two towers. However, the two-tower method is far less accurate. Conversely, the more towers that are available in any given area the more accurate triangulated cellphone positioning can be.

Still, "pinpoint" is not the best word to use when describing the accuracy of any triangulation system. Many factors can cause the calculated results to be off, even when several cell towers are involved. The iPhone can still use even poor data, however, it makes a best guesstimation of your whereabouts and presents it on your screen as a large circle, and your actual position is somewhere inside that circle. As the data becomes more accurate that circle becomes smaller until it appears as a pulsing pinhead, meaning that you are getting the best GPS information the iPhone can give.

And even that isn't always very accurate. For instance, you'll sometimes see that pulsing blue dot moving through homes or wooded areas adjacent to the road you are traveling on in Google Maps. That's because something has skewed the GPS data. It could be anything, and the results can make for some pretty amusing moments. Usually, when better data arrives, the blue dot will slide to a more representative position on the map.

There are more things that can affect the iPhone GPS, but what it boils down to is this: 90 percent of the time (my estimation which is not backed up by any data other than personal observation) the iPhone's GPS works well regardless of the positioning method employed and, from what I'm told by friends with other devices, the iPhone often works better than other smart phones with GPS capability.

It's that ten percent of the time that bites you in the rump. If it's at night and you find yourself in a bad neighborhood, in most urban areas the iPhone will come to your rescue. There are enough cell phone towers around to provide good triangulation info so Google Maps should be able to offer you a route to environs more to your liking and you don't have to get out of your car. If, however, you are on a narrow, muddy road out in the middle of nowhere with water infested with God knows what on either side, and you've got maybe two bars on your cell's signal strength meter I would not expect my iPhone to give you a good GPS reading.

In fact, that's just what happened to me while on that muddy trail. With the iPhone in the car I could not get Google Maps or MotionX GPS to function. Every so often I'd stop and hang the iPhone out the window and I was able to get a satellite reading, which was somewhat heartening because I could at least tell someone my position. Of course, I would likely drained of blood by the time they found me because of the mosquitos and other blood suckers the inhabit Florida's deep woods.

(Note to self: Keep insect repellent in the car)

That muddy trail ended and I was able to turn around and go back the way I came. I did make it out alive and without having to call in the Marines. I think even they would have had a tough time dealing with the insects I saw out there.

My iPhone 3G's GPS didn't start getting any usable data until I was about 20 miles outside of Orlando.

By the way, MotionX GPS is a wonderful app if you have an iPhone 3G or 3GS. The app can display all kinds of info about where you are and where you've been. It even provides compass readings for iPhone 3G users, though you have to be moving at least 3 MPH in order for the compass to work properly. iPhone 3GS users don't have to worry, MotionX GPS makes use of the built in compass in your phones. If you hike, bike, or run you should take a look at MotionX GPS.

I should also mention that while using the GPS data on an iPhone, or any smart phone, it is the indirect use of GPS that make these devices worth having. Apps like Urban Spoon and Yellow Pages use GPS data to figure out what's around you and often the GPS data does not have to be terribly accurate for these apps to work, which is why the original iPhone worked so well.

So, the iPhone's GPS is more than adequate for most situations where you would need GPS, but not all. If your life depends on reliable GPS data or if you drive a lot then get a dedicated GPS device, something with an antenna that can grab satellite signals anywhere. If, on the other hand, you have only occasional and casual need for GPS then the iPhone 3G or 3GS should do you just fine.

Next time I'll take a look at the iPhone's camera.

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Paul in Brookline

Your reference to “different kinds of GPS” is incorrect.  GPS refers solely to the the use of the US DoD satellite based system (officially called GPSS).  The generic term you’re looking for is “geolocation”.  Geolocation refers to any means of determining the user’s position on the surface of the Earth.

GPS position accuracy is affected by a number of factors and, as you correctly noted, signal blockage is a primary problem, affecting users in vehicles and buildings.  GPS receivers can also be confused if they’re transported significant distances while turned off, since the internal satellite ephemeris will no longer accurately predict which satellites are in view.

Lee Dronick

Do what I do Vern, carry your old Navy sextant around with you. Your iPhone gives an accurate enough time and you can use one of the calculator apps to reduce your shots. smile

Seriously, if you are in the boonies and need help then providing the authorities with your position within a few hundred feet is better than having them search hundreds of square miles. Of course if you are under a heavy canopy of trees or big shrubs then that makes it harder to spot you. Always carry several signaling devices such as road flares, big piece of orange fabric (poncho), whistle, mirror (use one from the car), flashlight, strobelight (camera flash can substitute). Maybe even water dye marker that is often part of an aquatic life preserver.

Also if someone is a frequent hiker, backpacker, or explorer then one of the emergency locator beacons designed for those people may be a good investment.


Of course, the best-known use of GPS is single-purpose devices FOR driving. Unsurprisingly, they like to suggest mounting them on the dashboard or even suction-cupped onto the windshield so the gizmo has the best view of the sky.

You might try that next time you think it unwise to hold your phone out of the car. It won’t be perfect, but it can raise your odds of a good signal substantially.

BTW, of course you know that your Maps app will show you your location AND a satellite view that can help you correlate the blue dot to the particular muddy road—they don’t put ‘em every hundred yards—that you’re on. Case closed.

Chris Keller

All the comments are somewhat missing the “target”. In addition to the issue of sat reception, the iPhone uses Assisted GPS which is standard for cell phones. This service can require the cell service to be available to create a complete location. It creates a snapshot of sats and sends the details to a server to create an actual fix. Additionally, maps aren’t local. They require an internet connect.

Tik Tok

While there’s lots of talk here about the use of real GPS, using satellites, I’m pretty sure the iPhone 3G doesn’t use satellites for its location services.  The test I’ve employed for this is when I am routinely and totally out of cellphone range, which is not the situation Vern describes here apparently.  When you have no cellphone service, you get no response from the built-in Maps program.  No blue dot, no blue circle, no blue anything.  Similarly, any app which ordinarily seeks to locate you and provide something in relation to your location will not work. 
Apple disserves its customers by not pointing out this very significant difference between what it offers and what people think it offers.  I suspect that someone, sometime, will assume real GPS service from an iPhone and suffer real injury when, in the wilderness, no satellite service can be used with the device.
If I am wrong, please correct me, but my experience has been repeated in a variety of situations where no cell phone coverage exists.  If true GPS were on the iPhone, it would have shown up.

Vern Seward

Hi Tik Tok,

Actually, the reason the iPhone can’t use satellite for maps while the iPhone is out of cellphone range is because the iPhone downloads it’s map data from the Internet each time it needs it. No cellphone connect means no 3G or Edge connection, and so no maps and no location service.

The true test of your scenario would be to have WiFi available, but no cellphone coverage. I think you’d find that if you are outdoors in the aforementioned situation that the iPhone’s satellite GPS system would work just fine and give you your location on a map downloaded via WiFi.

You can also test this by using an app that provides full GPS readings like MotionX GPS or others. What you’ll find here is that you’ll get log. and lat. readings from the satellites and, if the app caches a map, a nice blinking dot. Other location services won’t work because, again, there won’t be any Internet access and so, no location aware data.

I should have included the above situation in my article. I apologize.

Apple employs “true GPS”, it’s just that the supporting services may no always be available.

Vern Seward


Part of your problem with in-car GPS may be your windshield. Many newer cars have a metalized windshield that helps keep solar heading down. You will not get much of a signal through such a windshield. We rented a car in Europe with a giant metalized windshield and my TomTom was useless unless we held it near a side window. Easy check: Motion-X shows the GPS signal. See what it is in the clear and when it is in the center of the inside of the windshield. If there is a noticeable change, that’s your problem.


No cellphone connect means no 3G or Edge connection, and so no maps and no location service.

I have xGPS installed on a jailbroken iPhone, a program which allows you to download Google maps tiles for future use offline, but even with this the iPhone GPS won’t find your location without cellular service. With this being said, I’m unsure how Apple can advertise GPS as a feature if it’s less use than a $100 Garmin.

The above sceanario can be tested on regular Google Maps by the way since it stores recently browsed maps in the phone’s cache.

Vern Seward

Hi KC74,
The whole point behind the xGPS app is to get you usable GPS features even when you are not able to download maps real time. In fact xGPS site states that, “to use xGPS as a “real” GPS you will need an iPhone 3g, or an external GPS module to add to your Ipod Touch”

There’s also this:
“Offline Mode: Prevents xGPS from using the data connection (Internet). Turn this on if you have a limited data plan and don’t want to exceed your allowance, or if you are roaming and don’t want to pay for roaming fees. This setting prevents xGPS from automatically downloading any missing map regions and forces it to use existing maps that are already downloaded. xGPS will also not complain about Internet access while in this mode.”

The app also indicates that it can be used on an iPod Touch with a GPS module attached, and that any of several types of GPS systems can be used on the iPhone.

I suspect you may have something not set correctly in your xGPS app, but this seems to indicate that xGPS, and so the iPhone 3G, should work without cellphone service.

BTW, the earlier version of xGPS needed a data connection to plot routes, with the offline mode now available that should no longer be an issue.

I’m going to jailbreak my iPhone and try it.

If there’s an airplane mode on a jailbroken iPhone try turning that on and see what happens.

Vern Seward

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iPhone 3G finds your location via GPS or by triangulating your position using Wi-Fi and cellular towers. It also finds points of interest by keyword: Search for ?coffee? and iPhone shows you every cafe nearby.Get directions to wherever from wherever. View turn-by-turn directions or watch your progress with live GPS tracking. Maps on iPhone shows you live traffic information, indicating traffic speed along your route in easy-to-read green, red, and yellow highlights.
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Bought this thing for my business for the GPS, but the instructions are clear as to activating the GPS nor the internet capabilities. Can anyone help me and what might the cost be?

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Bought this thing for my business for the GPS, but the instructions are clear as to activating the GPS nor the internet capabilities. Can anyone help me and what might the cost be?

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