How to Use a GPS Device in the Backcountry

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So last November I talked my dad into scouting a canyon system in the Prescott National Forest — we were probably 14 miles from any cell service, deep enough in that the satellite radio on my Garmin inReach Mini 2 was the only thing connecting us to the outside world. At some point on the descent I realized the drainage we were dropping into didn’t match what I’d memorized from the topo. Turned out we’d drifted about 600 meters east of our planned route without either of us noticing — the ridgeline looked similar enough from above that it didn’t register until we were already down in it.

I pulled up my saved track, identified exactly where we’d gone off course, and we were back on route in maybe three minutes. Dad had been staring at his phone the entire time getting zero bars.

That’s what this is really about. Not “should you get a GPS” — yeah, probably — but whether you actually know how to use one before you need it.

If you’ve been reading through our complete wilderness navigation guide, good. Map-and-compass skills are the foundation, and I’m not going to pretend a GPS replaces them. This is about adding the GPS layer on top of that foundation and not screwing it up.

Table of Contents

• Why Not Just Use Your Phone
• What a GPS Device Actually Does
• Setup at Home, Not the Trailhead
• Marking Waypoints in the Field
• Routes vs. Tracks: The Difference Matters
• Battery Math: How Long Will It Last?
• When GPS Gets Weird
• Things People Get Wrong

Why Not Just Use Your Phone

My brother asked me this last spring and I had to stop and actually make the case, because on paper a phone with downloaded maps sounds fine. Here’s the problem.

Phone battery under backcountry GPS conditions drops fast. I tracked this on my own phone over two trips: normal use gets me 8-10 hours, but GPS navigation with no cell signal running the whole time tanks it to 4-5 hours because the cellular radio is constantly searching for a tower. A Garmin eTrex 32x runs 25 hours on two AA batteries. Swap the batteries and you’re back to 25 hours. It’s not even a close comparison.

Then there’s the map problem. Phone GPS works offline only if you downloaded the right tiles ahead of time, and people forget. Two separate times I’ve watched other hikers discover this when they’re already in the field — phone out, maps app open, gray empty screen where the terrain should be. Dedicated GPS units keep their maps stored internally.

Accuracy is the third thing. Phones use what’s called A-GPS, which combines satellite data with cell tower and Wi-Fi signals to get a fast fix. In the backcountry with no cell service that assistance disappears, and you’re left with raw satellite triangulation from however many birds you can see from your location. My Garmin GPSMAP 66i pulls from GPS, GLONASS, and Galileo simultaneously — I’ve measured it averaging 2.1 meter accuracy against benchmark coordinates in open terrain. My phone hit 4.7 meters in the same spot and degraded to 8-12 meters under dense ponderosa canopy. More systems, more reference points, better triangulation. That’s just math.

What a GPS Device Actually Does

Okay I’m going to geek out for a second here because I think most people skip this and then wonder why their GPS feels confusing.

Your position display is showing your current coordinates — latitude/longitude or UTM grid coordinates depending on how you’ve set it up. UTM is better for using alongside a paper topo map because the grid math is easier. The unit also shows you how many satellites it’s currently locked to and an accuracy estimate. That accuracy number matters. I check it before I trust any position reading, especially in terrain where buildings or cliffs might be blocking part of the sky.

Waypoints are saved locations. You give them a name, they get stored with coordinates and elevation, and you can navigate back to them later. Simple concept, but waypoints are the tool that actually keeps you from getting lost — more on this in the next section.

Your track is the device recording where you’ve been as a continuous line of GPS coordinates logged at set time intervals. Think of it like a breadcrumb trail drawn on your map in real time. You can follow it backward to retrace your exact incoming route. I use this constantly. There’s something really comforting about being able to scroll back through your track and watch the whole morning’s route appear on screen.

And routes are planned sequences of waypoints with the unit actively guiding you between them — showing bearing and distance to the next point as you move. The distinction between tracks and routes trips people up. Track = where you went. Route = where you’re planning to go.

Setup at Home, Not the Trailhead

Do this the night before. Seriously, doing GPS setup at the trailhead is how you end up fiddling with settings when you should be hiking.

One thing that burned me early: coordinate datum mismatch. Most USGS topo maps are printed in NAD83 datum. Most GPS units default to WGS84. The positional difference between those two in the United States is under a meter, which is negligible for hiking purposes, but when I was first comparing my GPS coordinates to my paper map I spent like 10 minutes thinking my unit was broken before my dad explained what datums were. Just set both to match and move on.

Map quality is the other thing. The factory basemaps on most consumer GPS units are basically highway overview maps — totally useless for reading terrain. You need 1:24,000 scale topo tiles downloaded for the specific area you’re heading to. My Garmin syncs a 200-square-mile block in about 2 minutes. I do it the night before every trip while I’m packing.

One more: track recording interval. The auto setting saves battery by recording less often, but it can skip over switchbacks and short technical sections, which makes your track harder to follow back. I run 30-second intervals. The battery hit is maybe 10-15%, which is a fine tradeoff.

Marking Waypoints in the Field

Mark your trailhead before you walk away from your car. This is the most important habit and the one people skip most often because it seems obvious and then they’re standing in the dark 8 miles in trying to remember if they actually did it.

After that — trail junctions, creek crossings, ridge saddles, anything that would be hard to identify in low visibility or from a different approach angle. I usually end up with 4-6 waypoints on a full day hike and more on anything multi-day.

The naming thing matters more than you’d think. “WP001” tells you nothing at 2 AM when you’re cold and tired. I use short caps: TRAILHEAD, MAIN_FORK, RIDGE_COL, CAMP. Most Garmin units cap waypoint names at 10-15 characters so there’s no room for anything descriptive anyway.

Something I figured out on my own: on multi-day trips, mark a waypoint every morning before you leave camp. Not just your primary camp — each morning’s start point. That way if you get turned around on a side trip or a day hike, you can navigate back to that morning’s waypoint instead of trying to retrace miles of track. Sounds obvious in hindsight but it took me a trip to learn it.

Routes vs. Tracks: The Difference Matters

A route is a planned sequence of waypoints with active navigation — the unit shows you bearing and distance to the next point and updates as you move. When you arrive at one waypoint (within whatever arrival radius you’ve set, usually 15-30 meters), it automatically starts guiding you to the next.

To use a route you just select it and hit navigate or go. The unit starts showing bearing and distance to waypoint one. Here’s what catches people off guard: that bearing is always straight-line. The GPS does not know there’s a cliff between you and the waypoint. It’s your job to find the actual path. Use the bearing the way you’d use a compass bearing — pick a landmark in that direction, navigate to it, recheck your bearing. Don’t hike staring at the screen.

Tracks are different. A track is passive — it just records where you’ve been. Track-back navigation (following your track in reverse) is useful for retracing an exact route, but it isn’t always the smartest path home. If you clambered through a nasty talus slope on the way in, maybe there’s a better way out. Track-back shows you one option; your brain picks the actual route.

Battery Math: How Long Will It Last?

I can’t help myself here, I love this kind of calculation.

A typical Garmin GPS unit draws somewhere in the 80-120mAh per hour range with the screen on. Using 100mAh as a midpoint, and two 2500mAh AA lithium batteries (5,000mAh total): theoretical runtime is about 50 hours. Garmin’s spec is 25 hours on standard alkaline batteries, which makes sense — alkalines are rated lower and have additional cold-weather degradation built into those estimates.

Cold matters a lot. At 0°F, lithium loses roughly 30% of rated capacity — so that 50 theoretical hours becomes closer to 35. Alkalines at 0°F lose 60-80%, which is why I’ve basically stopped relying on them in winter. I built a little tracking sheet after my second year running GPS in cold weather and the lithium numbers are consistently much closer to rated spec.

Screen brightness is underrated as a power variable. Dropping from 100% to 50% brightness extends runtime by somewhere around 20-30% with basically no cost to usability in most conditions — backcountry daylight is bright enough that full brightness is overkill most of the time. And battery-save mode, which turns the screen off between GPS updates, can nearly double runtime on long days where you’re not constantly checking position.

My personal rule: below 25% battery I switch to battery-save mode unless I’m actively navigating something technical. The battery percentage indicator on most units skews optimistic — what reads as 15% could mean 30 minutes of use or 2 hours depending on temperature and activity. I don’t trust it past 25%.

When GPS Gets Weird

Deep canyons are the main reliability problem. The walls block satellite signal from large portions of the sky, and with only a few satellites visible your accuracy degrades fast. I’ve had 15-20 meter position errors in narrow slot canyons where I could see maybe 20 degrees of sky directly overhead. The satellite count display tells you everything — 8-12 satellites is normal and accurate, 3-4 means your position estimate is soft.

Heavy tree canopy is more manageable — usually just drops accuracy to 5-10 meters rather than causing real problems. Northern slopes under old-growth forest are consistently worse than open aspects, in my experience.

There’s also a less common issue called multipath error, which happens when satellite signals bounce off canyon walls before reaching your unit. When this occurs the unit can place you somewhere you physically aren’t — sometimes clearly impossible positions, like standing inside a cliff. If that happens, trust your eyes and your paper map, not the GPS.

I cross-check mine with my barometric altimeter (the weather station I built in 8th grade started this obsession, and now I carry a dedicated altimeter wherever I go). When my GPS altitude and my altimeter reading diverge by more than 50 feet in stable barometric conditions, something is off with my GPS fix. It’s a useful sanity check that has caught two genuinely bad position readings over the years.

Things People Get Wrong

Track-back is one option, not the only option. Your incoming track shows where you walked — that’s it. If the way you came wasn’t the best route, track-back leads you back through the same questionable terrain. It’s a starting point for planning your return, not an automatic answer.

Map updates get skipped constantly. Trails get rerouted, access points change, new wilderness restrictions go in. Garmin pushes topo updates regularly and the process takes like 10 minutes. I do it before any trip I’m not already totally familiar with.

People also under-mark waypoints by a lot. One waypoint at the trailhead and one at camp is fine for a route you’ve done a dozen times. On new terrain in complex country, one every mile or two keeps you from getting confused about which ridge you’re on if visibility drops.

And the battery thing: don’t assume the indicator is accurate. I got caught once with a unit that said 20% and died 45 minutes later in 20-degree weather. Now I treat 25% as empty and act accordingly.

The whole point isn’t having a GPS. It’s building habits around it — marking waypoints before you need them, setting up maps at home, understanding what the numbers are actually telling you — so when you’re 14 miles from the trailhead and something goes sideways, you’re just reading data instead of guessing.