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You are here: Home / Blog / GPS: The Good, The Bad, and the Ugly

GPS: The Good, The Bad, and the Ugly

by Rex Sanders on October 13, 2020 Blog, New Features

In GPS We Trust

Credit: Illustration by U.S. Air Force, public domain. Design by Rex Sanders.

Introduction

We trust the U.S. Global Positioning System (GPS) for accurate locations to help guide us through the wilderness – either through smartphones and similar devices or via paper maps with reasonably correct feature positions. Global Navigation Satellite Systems (GNSS), like GPS, have revolutionized position, navigation, and timing. Yet, they have a variety of physical limitations and human-caused problems that can lead hikers astray.

Backpackers can work around many GPS issues by maintaining spatial awareness. One shouldn’t just keep hiking until an expensive smartwatch tells you to turn. Instead, periodically match electronic or paper maps with real-life features like creeks, ponds, peaks, and passes. Then you might recognize when GPS is misleading you.

The Good

Good

The recently-created U.S. Space Force now runs GPS, including 31 satellites in orbit. With a clear view of the sky, smartphones, GPS mappers, satellite communicators, and even smartwatches can often determine your position to less than 6 feet (2 meters). Just a few decades ago, the best global radio-navigation system (Omega) was accurate to about 4 miles (6.4 kilometers), using a receiver bigger than a suitcase – plus a large antenna and a power supply. Many backpackers got much better positions using a good map and a cheap compass.

GPS satellites are also equipped to detect nuclear bomb detonations and relay Personal Locator Beacon (PLB) rescue messages.

The U.S. Federal Aviation Administration (FAA) operates the Wide Area Augmentation System (WAAS) using three geostationary satellites that cover North America. WAAS provides real-time corrections to GPS signals distorted by the atmosphere, and can more than double the position accuracy. The FAA designed the system to support aircraft, but most GPS devices used by backpackers include WAAS receivers. The European Union runs the comparable EGNOS system for Europe. Similar schemes improve GNSS accuracy in some other areas of the world.

Yet the U.S. Government continues to improve GPS technology. They’ve started launching the next generation of satellites, that by the late 2020s, using new receivers could give positions with three times more precision. Are you standing on the left side of the trail, or the right? And do you need a smartphone to tell you? The new satellites also include stronger signals and other technologies that will make getting an accurate position in dense forests even easier.

There are three other GNSS networks operating today. The European Union supports Galileo, providing 3.3-foot (1-meter) location accuracy from 22 satellites. The Russian Federation runs GLONASS, including 24 spacecraft supporting 9.2-foot (2.8-meter) positions. And finally, BeiDou, launched and operated by the People’s Republic of China, using 35 satellites to yield locations as good as 7.7 feet (2.3 meters). All three networks are planning or implementing upgrades to accuracy.

These systems work very similar to GPS. In fact, many devices can receive and process signals from multiple networks. Access to more satellites results in faster positions and better coverage in cities, forests, and canyons. However, devices in the U.S. may legally use only GPS and Galileo at this time.

The Bad

Bad

GPS and the other GNSS networks have their problems. Despite launching ever more powerful satellites, trees, buildings, and mountains can block the signals due to simple physics. Solar flares can scramble satellite messages. And GPS radio waves can bounce off buildings and mountains creating multipath errors, potentially offsetting your reported location by hundreds of yards (meters). Smartphones and similar consumer devices are especially vulnerable.

Your GPS position might not match what’s on your map for many reasons. Every map uses a datum or simplified mathematical model of the Earth’s shape, and there are several available. But if your smartphone reports your latitude and longitude, or UTM coordinates, using a different datum, your plotted position can be off by many yards (meters).

Plus, maps can have errors. Even USGS Topo maps have varying standards for accuracy. That peak you are standing on might look like it’s still many yards (meters) away on your GPS device; yet another reason to trust your lying eyes instead of a smartwatch.

Of course, all GPS devices require batteries and electronics that can fail in many ways. You don’t want to be staring in disbelief at a blank screen deep in the backcountry if that’s your only means of navigation.

The Ugly

Ugly

Even worse, human activities can jam or spoof GPS – intentionally or unintentionally. Jamming happens when another radio signal on the same frequency overpowers the message you are trying to receive – and GPS signals are notoriously weak. Spoofing is when someone sends fake GPS signals that lead you astray. But spoofed and jammed radio waves don’t stop at one receiver.

Jamming

Jamming is much more common than you might think. Drivers use cheap but illegal GPS jammers to prevent the tracking of trucks and cars. One truck with a jammer, parked next to Newark Liberty International Airport in New Jersey, interfered with aircraft landings until authorities tracked it down. Even cars and trucks with jammers traveling on nearby highways cause problems. An illegal jammer left running in a car parked at a trailhead with good views could block GPS signals for a large area.

Three poorly designed amplified TV antennas made GPS useless for ships, boats, and researchers at Moss Landing harbor in California, triggering a lengthy investigation. A rural TV antenna could have the same impact on hikers, especially if mounted high enough to pick up distant stations.

Military jamming exercises in the U.S. have caused many problems for civilian airplanes, including leading some of them off course. BPL community members occasionally report GPS issues at the same time they see military aircraft overhead.

What’s even scarier is that when we get self-driving cars, GPS jamming could cause nightmares on the way to and from the trailhead.

Spoofing

For many years, experts considered GPS spoofing too hard to pull off effectively. But now step-by-step instructions using inexpensive parts and open-source software are on YouTube. There are multiple reports of spoofed boats, ships, planes, drones, trucks, and cars going off course.

An accidental spoofing attack at a GPS conference in Portland, Oregon scrambled many smartphones in unexpected ways, some for several hours even after the transmissions stopped. Most phones reported a position in France until experts took extraordinary measures to reset the device. Even the U.S. military is looking for non-satellite navigation systems as backups to GPS.

Hackers could potentially install a GPS spoofing app on your smartphone or smartwatch without your knowledge. These apps trick your device into showing an alternate location, without sending radio waves. Some people deliberately install one to fool a workplace-installed tracking app or gain advantages for delivery drivers. These apps are also favorites of some Pokémon Go players. A long-forgotten or well-hidden app could cause serious problems in the backcountry.

Conclusion

GPS and similar systems are remarkable technologies that have transformed many hidden and visible parts of modern life. I wouldn’t want to go back to pre-GPS position, navigation, and timing for many reasons.

However, GPS problems can be much more than an inconvenience for backpackers mindlessly following smartwatch directions. If you ever activate a PLB or press the SOS button on a satellite communicator, these devices also send your GPS position. While that’s normally a huge help for search and rescue teams, there are many reports of inaccurate GPS locations leading them astray – or even forcing them to give up the search entirely.

It’s important for trekkers to stay found almost in spite of multi-billion-dollar navigation systems, $1,500 smartphones, and matching $900 smartwatches. We need to use GPS networks and GPS-dependent devices wisely, recognizing when they mislead us, and staying safe when they fail. A simple paper map, an inexpensive compass, and a few easy-to-learn skills can turn a potential disaster into an inconvenience.

More Information

GPS.gov

https://www.gps.gov

A wealth of information for the general public and professionals.

GPS report cards

https://www.nstb.tc.faa.gov/DisplayGPSReportCardArchive.htm

The FAA publishes monthly updates on the accuracy and availability of GPS.

Official GPS jamming or spoofing notices

https://www.gps.gov/support/user/

The U.S. government usually warns of planned GPS disruptions. Some other countries (including the UK) provide similar notifications. Worth checking just before you head into the wild.

Related Content

More by Rex Sanders

  • Rex takes on sleeping bag ratings in this installment of his monthly column Standards Watch.

Review

  • Ryan Jordan’s in-depth review of the Garmin inReach Mini
  • Andrew was disappointed by the Spot X

Forum

  • Our community gets into a spirited argument over the role of electronics in the backcountry

DISCLOSURE (Updated November 7, 2019)

  • Some (but not all) of the links on this page may be “affiliate” links. If you click on one of these links and visit one of our affiliate partners (usually a retailer site), and subsequently place an order with that retailer, we receive a small commission. These commissions help us provide authors with honoraria, fund our editorial projects, podcasts, instructional webinars, and more, and we appreciate it a lot! Thank you for supporting Backpacking Light!

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  • Oct 13, 2020 at 9:59 am #3679493
    Backpacking Light
    Admin

    @backpackinglight

    Locale: Rocky Mountains

    BPL author Rex Sanders tackles the pros and cons of navigating by GPS in a short blog post that includes links for further info.

    • GPS: The Good, The Bad, and the Ugly
    Oct 14, 2020 at 10:17 am #3679660
    Mark Wetherington
    BPL Member

    @markweth

    Locale: Western Montana

    Good article. I don’t use GPS and there’s only been a few times in over a decade of backpacking (including lots of off-trail hiking in the West and Southeast) where I’ve really wished I had it.

    Once when I was hiking up in the middle of winter to an abandoned lookout tower to spend the night and had some navigational issues and ended up bivying in -5 F temps (which I was prepared for, but not excited about) only about .1 miles from the lookout. If I’d had the GPS location I would’ve kept going rather than calling it quits after I became exhausted and it got dark.

    The other time was in a recently burned area in the Wenaha-Tucannon Wilderness in WA/OR where the trail totally disappeared in new growth. I got pretty turned around up there but was able to re-orient myself eventually. It was a long day and I was more frustrated by the slowing of my pace than any real sense of “danger”.

    Both times I ended up with memorable experiences (and entertaining stories) and, since I was prepared for things not going according to plan, there wasn’t any real risk involved. “Make plans, but don’t plan on them . . . ” and all that.

    I suppose what I’m most curious about in regard to GPS (as someone who has no immediate plans to incorporate it into my hiking gear collection) is the impact it has on the experience of the user. Mostly in regard to the actual cognitive process of navigation, immersion in the landscape, situational awareness, and overall appreciation of the experience. I tend to skew more the side of engaging in backpacking as an “art” rather than a “science” and I savor the mystery of not knowing if I’m a mile away from the lake I’m trying to reach or 0.893 miles away. I’ll get there when I get there and it will be beautiful; there’s no satisfaction I gain from the details.

    An acquaintance of mine who was a long-time environmental professor at University of Idaho and led semester long field trips based out of a research station in the Frank Church-River of No Return Wilderness said that there was a profound difference among students when just looking at plot sites on GPS vs. pulling out a topo map and seeing how everything connects — watershed to watershed, plateau to peak, etc. The GPS was useful for the specificity of science but obscured the “big picture” view of things, at least in his estimation.

     

    Oct 14, 2020 at 11:09 am #3679666
    Andrew Marshall
    Moderator

    @andrewsmarshall

    Locale: Tahoe basin by way of the southern Appalachians

    There’s a really good podcast episode (I think of Hidden Brain) about an American tourist in Scandinavia who followed a car GPS deep into total wilderness despite lots of hints he was on the wrong track (increasingly bad roads, etc). Thanks Rex for all this info – it totally filled in some knowledge gaps for me.

     

    Oct 14, 2020 at 11:15 am #3679668
    idester
    BPL Member

    @doug-i

    Locale: The Cascades

    “Wenaha-Tucannon Wilderness in WA/OR where the trail totally disappeared in new growth.”

    I wonder if that was the same trail I ‘suffered’ through last year. Completely overgrown for a number of miles, didn’t look like anyone had been on that trail for years, lots of downed trees to climb over/under. I had gps and it didn’t help. :-) My hiking partner lost his gopro on that trail. An interesting trip.

    Oct 14, 2020 at 12:30 pm #3679686
    Mark Wetherington
    BPL Member

    @markweth

    Locale: Western Montana

    Andrew — pretty sure I heard that podcast, too. It was an interesting story, for sure. Outside Magazine also had a similar story about the phenomenon that is well-worth reading: https://www.outsideonline.com/2135771/your-gps-scrambling-your-brain

    “What, we wonder, is our now habitual use of navigation tools doing to our minds? An emerging body of research suggests some unsettling possi­bilities. By allowing devices to take total control of navigation while we ignore the real-world cues that humans have always used to ­deduce their place in the world, we are letting our natural wayfinding abilities languish. ­Compulsive use of mapping technology may even put us at greater risk for memory loss and Alzheimer’s disease. By turning on a GPS every time we head somewhere new, we’re also cutting something fundamental out of the experience of traveling: the adventures and surprises that come with finding—and losing—our way.”

    It focuses most on use in non-wilderness settings, but does touch on its use in the backcountry a bit.

    It noted that GPS might be making the backcountry safer (a good thing!) as SAR calls in national parks had dropped from 2004-2014. I’d be curious as if SAR calls are lower now than in 2014 since use of national parks has increased and many new visitors are often underprepared for the realities of wilderness areas, with some relying on their phone or PLB as  bail-out option.

     


    @doug-i
      The trail that I got lost on was around Smooth Ridge, above Fairview Bar. I could follow the trail well enough from Fairview Bar up to the ridge (finding its start was a bit hard, but the switchbacks were pretty distinct). Once I got on the ridge it was a mess and I didn’t reconnect with the trail until a mile or more later, that took me about 2 hours to get to. It was a long day for me as I had planned to hike from Fairview Bar to Oregon Butte and getting lost just made it feel that much longer. If you found a bandana and a Write-in-the-Rain notebook out there it was mine — I slipped on a downed tree and the bottom of my cargo pocket ripped without me knowing, so I didn’t realize I had inadvertently littered until later.

     

     

    Oct 14, 2020 at 2:16 pm #3679713
    Ben C
    BPL Member

    @alexdrewreed

    Locale: Kentucky

    I have always carried a printed map but rarely look at them any more. It’s becoming more rare every trip. There are a few reasons.

    • First, ease of  access. My phone is always handy in my pants pocket. A printed map is typically in the front pocket of my pack, so I have to take off my pack to see it.
    • Second, it almost always puts me on the map, so that I can easily see where I am.
    • Third, it becomes obvious much more quickly if I get off my intended route.
    • Fourth, in the rare situation where I can get a satellite fix, its still a good map. I usually fin it easier to read for most purposes than a printed map.
    • Fifth, if I’m ever a little confused as to what peak/pass/etc. is what, gps makes it pretty obvious.
    Oct 14, 2020 at 8:43 pm #3679776
    Arthur
    BPL Member

    @art-r

    To add to Ben’s list

    • Sixth.  I carry a real camera for its higher quality photos.  I can download the gpx file and easily add gps points to my pictures after the trip. It’s fun to relive the trips years later and see my pace, distance each day, etc.,  and pull up the pictures to enhance the memories and places.
    Oct 17, 2020 at 6:37 am #3680060
    Bob Kerner
    BPL Member

    @bob-kerner

    I can’t imagine not using both a GPS and a map. My hiking frequency has increased lately and I have encountered quite a few people on the trail using phone based GPS and they cannot reconcile what the phone tells them with what terrain they are on. “Can you tell me where the trail is?” was The most common interaction I had last weekend. Followed by “Where is the road?”

    I don’t start a trip without 3 mapping sources: I start with a guidebook and sometimes photocopy the small guidebook map of the trip; then the regional paper map goes in my pack; finally the route on Gaia in my pants pocket. Gaia has saved my bacon twice recently where markers were down or missing and knowing my ‘precise’ location helped me find the concealed intersection of trails.

    I worry about people new to hiking that are out there with only their phone and no understanding of how GPS works or how to read the map on the phone.

    Oct 17, 2020 at 10:57 pm #3680141
    Sam Farrington
    BPL Member

    @scfhome

    Locale: Chocorua NH, USA

    “I worry about people new to hiking that are out there with only their phone and no understanding of how GPS works or how to read the map on the phone.”

    I’ve often met these folks, and try to be as helpful as possible. This year the NH White Mountains seem to have attracted an onslaught of visitors.  Fortunately, many of the rescuers are volunteers; otherwise Fish & Game and the Forest Service would probably go bust.  I think it is because folks in more heavily populated areas would just like to get to someplace outdoors where they can enjoy the fresh air without a mask on.  I feel the same, but don’t have to travel to get to my bushwhacking routes where I see nobody, ever.  And they are great practice for areas where designated trails have not been maintained and have grown over as mentioned above.

    Like the first poster above, I don’t use GPS.  Have read many manuals, and learned a lot, but not the skills needed to dispense with laminated sections of USGS paper maps.  There have been a number of trainings, but they all cost several hundred dollars, not in my budget at the time.  For me, the maps are also essential for planning long distance hikes, and if there is a problem, having a ‘big picture” to find routes to the nearest highway.  So carry trail maps of the entire region, along with the more detailed USGS sectioned maps.

    Rex Sanders’ article scares me a bit about getting trained.  Do carry a little Garmin 301 to record points for others’ reference, and a PLB, the smallest and lightest I could find.  The 301 has a screen to select the datum of the map.  Am surprised that a smart phone app would not have the same.

    Used a PLB only once, and it brought the K9 deputy and his dog, Ivan, to a parking lot over 50 yards away.  Fortunately, the PLB was an older model with a strong flashing light, and the deputy was just leaving when he spotted it.  He told me some hikers use PLBs in the middle of nowhere.  My shelties were scared ____less to get in the back seat of the cruiser with Ivan, until they realized he could not get out of his cage.

    When recording waypoints, I’ve often noticed that the coordinates change later in the day, even standing in exactly the same place.  So Rex is probably right about the error potential.   But it is not so much about perfect accuracy as about how close the GPS gets.  Except maybe for rescues in heavy storms, for someone badly injured, and their location must be pinpointed.  Just such occurred in the Whites some years ago, and a fatality resulted.

    I know one thing, I’ll never drive or even ride in a self-driving vehicle unless it’s a hearse, in which case it won’t matter.

    Oct 17, 2020 at 11:55 pm #3680144
    Pedestrian
    BPL Member

    @pedestrian

    A runner ended up running a 49 mile marathon because of a GPS app failure……

    A GPS failure meant this runner completed 49 miles in the virtual London Marathon

     

     

     

    Oct 19, 2020 at 8:48 am #3680259
    Ben C
    BPL Member

    @alexdrewreed

    Locale: Kentucky

    I suspect hundreds have done the same without GPS. I really find it reliable and easy to use. A GPS makes it MUCH more likely that I don’t do extra miles. Most times I have gotten off route, it has been my phone GPS that has shown me my error.

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