Working with Bearings and Your GPS

How bearings and a GPS work together

In modern land navigation, the GPS and the compass divide the labor. The GPS is excellent at telling you where you are and which direction a destination lies — it can compute a bearing to any waypoint instantly. The compass is excellent at holding that direction as you walk, especially under trees, in a canyon, or anywhere the GPS's own sense of direction gets shaky. The skill is reading a bearing off the GPS and then handing it to the compass to walk. This is the GPS-forward approach to land navigation, and it's faster and more reliable than either tool alone — but only if you understand the few distinctions below.

Bearing-to-waypoint (GoTo) vs. compass bearing

When you tell the GPS to navigate to a destination — a "GoTo" — it gives you a bearing to the waypoint: the direction, as an angle, from where you stand to that point. That number is a calculated bearing — the GPS computes it from your current location and the waypoint's location, and reports it relative to whichever north reference the GPS is set to. A compass bearing is the same kind of angle, but as your magnetic compass measures it. The two will only agree if the GPS is reporting the angle in a north reference your compass can match (more on that below). Conceptually they describe the same line; the question is always measured from which north?

Course vs. bearing — they are not the same

Two words the GPS uses that beginners blur together:

• Bearing is the direction from your current position to the waypoint. The GPS recalculates it — and the distance — every time your position updates, so it always points at the target from wherever you actually are.
• Course is the direction of the straight line between your starting point (A) and the destination (B). It's the fixed line you'd follow to go straight there.

The recalculating bearing is one of the biggest reasons to navigate to a waypoint with a GPS instead of with a fixed compass bearing and distance. A compass bearing and distance describe only the straight line from A to B; step off that line to get around a cliff, a thicket, or a swamp and the number no longer points at your target. The GPS's bearing isn't tied to a line — it points from where you are to where you're going. You can detour around obstacles all day and still have a usable bearing and distance to the target.

Most of the time that's exactly what you want: reach B by whatever path the terrain allows. Occasionally, though, you need to stay on the actual line between A and B rather than just arrive at B by a less direct path. That's when course matters. Two ways to hold it:

• Note the initial bearing and keep matching it. When you start, read the bearing to the waypoint and remember it. As you travel, keep the GPS's recalculated bearing equal to that initial number — as long as the two agree, you're still on the original A-to-B line. Drift to one side and the recalculated bearing will no longer match; that's your cue you've left the line.
• Navigate a route and watch the course deviation indicator. Set the leg as a route and the GPS shows a course deviation indicator (CDI) — how far off the line you are and which way to step back onto it. This is the more advanced technique.

Turning a bearing and distance into a waypoint (projecting)

Sometimes all you have is a bearing and a distance — "the cabin is 1.2 miles at 340°" from a description, a report, or a landmark you've sighted but can't reach. You don't need its coordinates to navigate there with the GPS. Most units have a project waypoint feature that builds the destination for you:

1. Mark a waypoint at your current location.
2. Run the project-waypoint feature on that mark, entering the bearing and distance.
3. The GPS computes the coordinates of that point and saves it as a new waypoint.

Now GoTo the projected waypoint and you get everything above — a recalculating bearing and distance from wherever you actually are, so you can detour around obstacles and still home in on the target. Projecting is how you turn a one-shot "bearing and distance" into a destination the GPS can actively navigate to. Enter the bearing in the same north reference your GPS is set to (see below), or the projected point lands off in the wrong direction.

Heading is where you're pointed, not where you should go

The GPS also shows a heading — the direction you are actually moving (computed from successive position fixes) or, on units with a magnetic sensor, the direction the unit is pointed. Heading answers "which way am I going?", bearing answers "which way should I go?" You steer by turning until your heading matches the bearing. Note that a movement-derived heading needs you to be moving to be meaningful — stand still and it goes nonsense.

Set the right north reference, or every angle is wrong

A bearing is only meaningful relative to a north. Your GPS can report directions referenced to True North, Magnetic North, or Grid North, and you choose which in the setup. This is the single most important setting for making the GPS and compass cooperate: if the GPS reports bearings in True North but your compass reads Magnetic North, every bearing you transfer will be off by the local declination — possibly many degrees. The fix is to decide on one north reference and set the GPS to it. See North References (True, Magnetic, Grid) and Declination for the three norths and GPS Setup for Map Coordinates for where the setting lives.

Walking a bearing the GPS gives you

The field procedure ties it together — and the key move is that you don't have to keep the GPS in your hand the whole way:

1. On the GPS, start a GoTo to your waypoint and read the bearing.
2. Set that bearing on your compass, then put the GPS away.
3. Follow the compass: sight along it to pick a landmark on that line, walk to it, and repeat. The compass holds the line just fine on its own — no batteries, no waiting for fixes, reliable under tree cover and in canyons where the GPS struggles.
4. Every so often, pull the GPS back out, read the current bearing (it will have shifted as you've closed in or drifted around obstacles), reset your compass to that new number, and put the GPS away again.

That rhythm — get a bearing, walk it on the compass, re-check periodically — is the everyday GPS-forward technique. The GPS does the math and gives you a fresh, recalculated bearing whenever you ask; the compass does the steering between checks. You get the GPS's accuracy without draining its battery or staring at a screen while you walk. For the broader picture of GPS in the backcountry, see GPS for Land Navigation; for the compass side of bearings, see Compass Bearings.