GPS Usage: One Expert's Observations

Steve Wood is an REI Outdoor School instructor in the San Francisco Bay Area and a founding member of Geocachers of the Bay Area, a regional geocaching club. Steve teaches beginning and advanced GPS courses for the REI Outdoor School. Here he shares insights on a variety of GPS topics, including a few issues that can confound first-time GPS users.

Q: What makes you such a big fan of GPS receivers?

A: It's a very useful navigational tool. I'm an ultralight backpacker. I save ounces everywhere I can, but on every trip I always bring a big 8-ounce chunk of technology with me—my GPS—because I find it to be very helpful. It records my travel accurately and provides quick data to help me make better choices along the way. If you've ever had to try to find your way along a faint or nonexistent trail, a GPS can be a real pleasure to use.

Q: First-time users sometimes find handheld GPS receivers to be daunting. What's the most common challenge people encounter when they're learning to use a GPS in the field?

A: If you've bought a GPS because you've never understood how to use a map and compass and you easily get lost, that's the wrong idea. To navigate safely in the outdoors, you must start by getting a good understanding of a map and compass.

Q: So I can't leave my map and compass at home?

A: A GPS does not replace a map and compass. It augments their use, and it can make some tasks much simpler. A GPS is very useful in whiteout conditions or in darkness. But a map and compass are still the essential tools. Unlike a GPS, they don't rely on batteries and they work in all conditions. Any battery-operated gadget can fail you.

Q: What kind of realistic expectations should a first-time GPS user have?

A: The biggest mistake people make with a GPS is thinking that it's all-knowing, that it's going to tell them how to get home. When you take it out of the box, take it outdoors and turn it on, it's going to do exactly what it should do: identify your present position. You don't have to set any settings or do any programming to it. It will identify your current position. The trick comes in understanding what to do with that information. Your GPS manual will tell you things like what the buttons do and where the different menu options are, but it doesn't tell you how to integrate this with traditional navigation, or even why you would want to bring a GPS on a trip. In some ways, manuals can actually confuse people. I recommend picking up a book on traditional navigation.

Q: Where do people often go wrong with a GPS unit?

A: Some people want a GPS to do too much. They go into the backcountry with a GPS alone and trust it fully. They pay too much attention to their GPS and not their surroundings. Without getting into route-building, all a GPS can do is point you, as a crow flies, to your destination. It can't tell you that there is a canyon and a cliff and a stream and a freeway and everything else between you and that spot. From your position you need to use a map and all your navigation skills to be able to use that information.

Q: How do you turn students and novices into better GPS users?

A: First we help them overcome the fear factor of a new technology. Secondly, we go into the 4 main things a GPS does. Then we turn the GPS on and talk about the different screens. GPS receivers display a lot of information, but I believe there are only 3 screens you need to focus on. If you're walking on flat land, why do you have the altimeter on? But everyone has the altimeter on. I use it maybe twice a year.

Q: What 3 screens are most valuable to you?

A: The satellite, compass and map screens.

• Satellite screen: It tells us about the position of the satellites overhead, which is critical to how well the GPS will triangulate, and helps you determine if your surroundings might affect GPS reception. If you've got reception, you can mark your position.
• Compass screen: Once a waypoint has been selected, this screen gives you direction and distance. It's intuitive to use, and comforting to follow a pointer while you watch the distance count down.
• Map screen: This helps you relate your position to a paper map, and shows the relative positions of waypoints to your current location. While we're moving, we can look at the track the GPS is recording of our hike.

Q: So how can a GPS improve backcountry navigation?

A: A GPS answers a few questions: What is your location? Where is your destination? How far is it? In what direction do I need to travel in order to reach it? Once you have asked the GPS those questions and it has answered, you're done. You should put it away and you should start looking around and thinking, "How can I get to that destination?" In classes I see a lot of students try to use a GPS by kind of sticking it up to their nose and following this device with their face stuck down on the screen as they're hiking. First, they're going to fall off a cliff if they keep doing that. Secondly, they're missing important clues around them—trail junctions, the way a ridgeline curves, or information that could really help them make choices about how to get to their destination. You've got to limit GPS use to what it's good at—providing very simple, basic information. Then incorporate that into your whole navigation plan for the trail. Then it works very well."

Q: Let's come back to GPS screens in a minute. You mentioned that a GPS receiver does 4 main things. What are they?

A: A GPS is principally designed to do these 4 things.

• It marks your present location. It's going to tell you where you are right now on the globe. It gives you a set of coordinates, which is the language the GPS uses. It's a very accurate way of describing your position. That's the GPS's primary function.
• It allows you to enter waypoints. These are other distant locations that use the same coordinate system. Entering a waypoint is no more difficult than entering an address in your mobile phone or PDA.
• It allows you to navigate to any one of those points that you've created by giving you a direction arrow saying, "This is the direction you want to travel and this is how far it will be to that point." In the case of car navigation systems, it might also give you turn-by-turn directions. But basically, it's going to say, "From where you are right now, go this direction and this distance and you'll arrive at this point."
• It records all of your activity in the form of a tracklog. You can think of it as a breadcrumb trail. Wherever you've stepped, it's continually marking little points along the way saying that you've been here. That has several functions. That can help you find your way back when you're lost; help you see where you may have made a wrong turn; can record for other people's use a track that you've followed.

I find most GPS are actually pretty simple devices. The unit I use, the Garmin 60CSx, has been popular because it's intuitive to use. Mark your position? A button on front says "Mark." Find a location? A button says "Find." Very straightforward. I tell students to try using it without even opening the manual. You'll find you can probably do everything you'll ever going to do with a GPS without ever opening the manual. I recommend getting a good book on navigation that pulls it all together like Wilderness Navigation by Darran Wells, published by NOLS (National Outdoor Leadership School). That's a good place for students to start.

Q: Let's go back to screen choices. For example, you encourage your students to turn off the electronic compass in a GPS. Why is that?

A: In my personal experience, I find the GPS-based compass, which is different from the unit's electronic compass, to be adequate for the task. The electronic compass in a GPS is designed so that if you're standing still, it knows which way your GPS is facing. So if you want to know, "Where is the point where I want to travel?" and you're standing still, it will point you in the right direction relative to where you are presently facing. If I turn the electronic compass off, I can turn the GPS any way I want and the arrow just follows the GPS around. It doesn't know which way you're facing. So it can't tell me which way to go. It is indicating the correct bearing on the compass dial, but it doesn't know where that actual bearing is relative to you. But the GPS itself, without that electronic compass, has a motion-activated, GPS-enabled compass. So if I just start walking, then the GPS says, "Ah ha! You were there. Now you're here. Therefore you're traveling in this direction." So the compass snaps into play when you start walking. As long as you're moving, that compass is very accurate. In my experience, it's more accurate than the electronic compass.

Q: Don't you find the altimeter screen and other screens helpful?

A: Yes, just not as much as the 3 key pages I mentioned earlier. You can configure the compass or map screens to show your elevation, so I don't really need to see altimeter page as a part of my page selection. And I can easily get to it in the main menu if I need it. You can know your elevation, for example, from other things. Garmin units specifically have a menu and a series of pages. Visualize it as a bookshelf and a stack of books. You can take that entire bookshelf and haul it around in your arms, but you're only really going to need the books that you're going to read right now. The rest are very handy, right there on the shelf. If you want them, you can get them. That's the idea of the menu system and the page system. Think of the page system as the books you're carrying in your hands. The menu represents the things sitting on the shelf. If you turn off anything from your page rotation, it sits in the main menu, and it's one click away to get to the main menu. Just one click and it's right there. So if I want to get to the altimeter, I just hit the "Menu" button, click "Altimeter" and I've got it.

Q: How many satellites do you need to acquire for a GPS to be effective?

A: You have to have 4. You need 3 to triangulate any time; you need 4 to get a 3-dimensional position. A GPS will report a 2-dimensional position (if it's only got 3 satellites, and it's pretty uncertain of where you are) or a 3-dimensional fix (with 4 satellites). So it knows your position and your altitude. Since the satellites move and come in and out of cover under trees, you really want more. You want 6 to 8 satellites so that you can move around and get under other obstacles. The more the merrier. In most conditions you should be able to get 8 or 10. That's pretty typical. When you have acquired a high number of satellites, you'll see that reflected in your accuracy estimate. With a lot of satellites, your accuracy may be as close as 10 feet.

Q: Is it common to acquire a high number of satellites?

A: Usually, yes. With a good, clear view of the sky, most of the time you will see 8 to 12. But satellites move, and every now and then I have seen very few displayed on the screen. I can't really say what's up with that, and experts in the satellite biz will certainly insist that such a thing is not possible, or at least likely. But a couple of years ago we taught some classes in Marin County up on Mount Tam, way up on a ridgeline with a perfect view of the sky. The students started complaining, "I'm not getting any reception." I'd say, "Give it time to find the satellites," But we started comparing units and there were few satellites on anyone's screens. We checked some more and there was just nothing. For about an hour, every satellite had set below the horizon. It happened for 2 consecutive Saturdays. Satellites came back up again in about an hour. I'm told by folks in the GPS industry that such a disappearing act can't happen, but that's what we saw. You can be on the top of a mountain without a tree in sight and get bad reception if the satellites are not cooperating. On rare occasions they just aren't in a position that works.

Q: That seems surprising, doesn't it?

A: Personal experience has taught me that some days are "good" satellite days, some are bad. It is surprising. So use the satellite screen on your GPS to determine what sort of configuration is overhead, and that will give you an idea of just how useful a GPS is going to be on that particular day.

Q: On those occasions when satellites are hard to find, what's going on in the sky?

A: The GPS constellation consists of a core of 24 satellites, plus a few specialty satellites. They're rotating in orbits that take them around the earth twice a day. They're constantly moving. During the day sometimes you'll have a real broad spread of satellites overhead at various levels above the horizon, and at all points of the compass. If you're going to do triangulation, that's what you want—satellites spread at broad angles. On occasion you'll find they're all grouped real low on the horizon. That will be a problem if you're down in a canyon—you're not going to be able to see any satellites. Or you might find them all to one side of the sky or in a line. Those positions will interfere with the ability of the unit to triangulate accurately. So it's possible to have issues with accuracy that are totally out of your control, issues that have nothing to do with your GPS or the terrain that you're in. It's just a matter of the positions the satellites are orbiting in that day.

Q: How can you tell where satellites are?

A: By looking at your satellite screen. A lot of students don't have the satellite screen in their rotation of screens. They've got it buried back in a menu somewhere. We have them pull that up. It's one of the major screens we have them look at.

Q: GPS accuracy is typically very good. How precise do you need it to be?

A: There are 2 ways of looking at that. When doing navigation in the woods, you often don't need great accuracy. If I'm navigating with a map and compass, I'm not trying to navigate within 30 feet of any location. Usually I'm looking for a mountain pass or campsite, and if I can get within 200 feet of it I can see my friend waving at me and find that location. So people need to stop focusing on this narrow area of accuracy that a GPS will promise you. It's not really necessary. Having accuracy within a couple of hundred feet can be OK. Now if you're using a GPS to pinpoint a very specific spot such as a geocache, then accuracy becomes more necessary. Yet in any sort of navigation, you don't have to know where you are within a couple of feet. A GPS will typically guide you to within 20 or 30 feet of your destination. But even if it got you to within 50 to 100 feet, you should be able to find a trailhead or your car or whatever it is you're looking for.

Q: Even with the limitations you mentioned, you never travel in the wilderness without a GPS, correct?

A: I always bring it. As I said earlier, it can be a real pleasure to use. Most of the time, it's totally reliable. You just have to remember: It has to be used with a good map, and you have to understand how to integrate it with your map for it to be a useful tool.

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