GPS for Land Navigation

What GPS does for a land navigator

A handheld GPS receiver answers one question precisely: "what coordinate am I at right now?" Combined with the skill and knowledge to plot that coordinate and you have a fast and accurate way to answer the "Where am I on my map?" question. It works in the dark and other low visability situations where more traditional navigation techniques may be difficult or impossible. Everything else useful a recreational GPS does for a hiker — waypoints, tracks, routes, ETA estimates, distance-traveled — is built on top of that one capability.

For land navigation specifically, that means:

• You can plot your position on a paper map. GPS gives you the coordinate; you walk it back to a point on a map. See UTM Coordinates and Latitude and Longitude for the two coordinate systems most receivers can output.
• You can mark places you want to remember. Trailheads, water sources, the spot you parked. Waypoints are the receiver's stored coordinates with names.
• You can navigate toward a stored coordinate. Type or import a destination's coordinates and the receiver shows you a bearing and distance to it. Doesn't pick the route — you still do that with the map and your eyes.
• You can leave a breadcrumb trail. Track logging records where you've been. Useful for retracing your steps and for telling the next group what the actual route looked like.

What a GPS does not do: pick a walkable route, read the terrain, warn you when the map is wrong, or replace a working understanding of Map Reading. It's a tool that delivers a coordinate; you do the navigating.

What every recreational GPS user needs to know

Setup decisions matter before you start:

1. Coordinate system. UTM, MGRS, USNG, or lat/lon. Pick the one that matches the printed grid on the map you're using. See GPS Setup for Map Coordinates for the full setup walkthrough.
2. Map datum. WGS84 is the modern default; older maps and surveys may be NAD27. Mismatched datums offset coordinates by 100m+, which is exactly enough to put your plotted position in the wrong drainage. See Map Datums.
3. Battery strategy. Spare batteries (lithium AA are the standard for hiking-grade receivers) and the habit of turning the unit off between fixes — that keeps a set lasting months.

For the deeper coverage of these decisions, see the GPS Setup for Map Coordinates concept.

Categories of GPS

The main categories:

• Dedicated handhelds (Garmin eTrex, GPSMAP, Oregon families; similar from other brands). Built for hiking — long battery life, rugged, button-driven, readable in sun. The mainstream of recreational GPS for the last 20 years.
• Smartphone GPS apps. Use the phone's built-in GPS chip plus offline-cached topo maps. Excellent display, much weaker battery story, fragile in cold and wet. Increasingly capable; not yet a full replacement for a dedicated handheld in serious backcountry.
• GPS watches. Convenient, weak at coordinate-display tasks, useful for tracks and waypoints if you live in the watch ecosystem.
• Satellite messengers with GPS (Garmin inReach and similar). GPS plus two-way satellite messaging. Different design center — emergency communication first, navigation second.

A smarthpone GPS app is a great low to zero cost way to learn to use a GPS. App quality varies widely, make sure the app you choose supports the coordinate format you want to use, the map datum your map uses, has the ability to create stored waypoints, and supports pre-loaded offline maps. A good smartphone GPS app is plenty of GPS capability for day hiking and easy weekend trips. It's also a good backup for a dedicated handheld GPS.

When you are doing longer trips, or trips in challenging conditions, most people ask the question is "which dedicated handheld do I buy?" — see the buying-a-GPS guidance.

Accuracy realities

GPS accuracy in open terrain is around 3–10 meters with a modern receiver; under tree cover or near cliffs it degrades to 10–30 meters; in deep canyons or under heavy canopy it can degrade further or lose lock entirely. See GPS Accuracy for the detailed treatment.

The practical implication: a GPS coordinate is a square, not a point. The reported precision (the digit count) often suggests more accuracy than the receiver actually has. A coordinate ending in ...832m E 683m N displayed to 1-meter precision is plausibly accurate to ~10 meters — useful, but not "this exact rock."

When the GPS dies

There are three primary failure modes.

1. The user forgot how to use the GPS or has it set up incorrectly.
2. The GPS receiver runs out of batteries or has some other sort of failure.
3. The GPS system itself is being tampered with or has been turned off.

The first one is on you. You need to know how to use your tools. The second one is less of an issue as the cost of GPS receivers drops. A hiking party is now likely to have several GPS receivers between them. Especially when you include the smartphones and GPS enabled watches. The third one is becoming more common in parts of the world with active military combat. There are alsoa few unlikely scenarios where large swaths of the globe could loose GPS coverage.

That's the case for a fallback — not a reason to distrust the GPS. Rely on it as your primary tool, and keep the underlying Map Reading skill (plus a backup device or a paper map) so a failure is a detour, not a crisis.

This is also why it's worth building your Map Reading and Compass Bearings skills along with your GPS skills.

Your car could quit working. That's not a good reason not to rely on a car for transportation. But it is a good reason to not forget how to walk.

How GPS works (briefly)

You don't need this to use a receiver, but it's where the accuracy — and the failure modes — come from.

The system is a constellation of about 24 satellites in six orbital planes, arranged so at least four are above the horizon anywhere on Earth, any time of day. Each satellite carries an atomic clock and continuously broadcasts a coded signal stamped with the exact time it was sent.

Your receiver measures how long each signal took to arrive and multiplies by the speed of light to get its distance to that satellite. One distance puts you somewhere on a sphere around the satellite; a second and third narrow that to a small "error triangle"; and a fourth both pins down the position and corrects your receiver's cheap clock — the satellites' clocks are exact, yours isn't, but its error is the same for every measurement, so four satellites let the receiver solve for it. Because each satellite also broadcasts its own precise orbital position (monitored and corrected daily by ground stations), the receiver can then compute where you are.

Two things worth carrying into the field:

• You need a clear line to at least four satellites. Canyon walls, dense wet canopy, or a metal roof block signals and weaken or prevent a fix.
• Satellite geometry matters. Satellites bunched in one patch of sky give a weaker fix than ones spread across it — which is why the receiver reports an estimated error (EPE), not just a position.

See the How the GPS System Works slides below for the diagrams.

Where coordinates come from when you don't have a GPS

A map with a printed grid is itself a coordinate source. You can read a UTM or lat/lon coordinate off the map by eye or with a measuring tool, and report your position to a partner who has a GPS. See UTM Coordinates for the reading-from-map technique. Both directions matter — map → coordinate and coordinate → map — because navigating successfully often requires bouncing between the two.