Do you still need a compass if you have GPS?

The usual argument for carrying a compass is that electronics fail. That is true, vague, and unpersuasive to anyone whose phone has never failed. The better argument is specific: each device has documented conditions under which it should not be trusted, and those conditions do not overlap.

Do you still need a compass if you have GPS?

Yes — carry both. Not because one is better, but because they fail differently.

The National Park Service puts navigation at the top of its Ten Essentials and defines it as map, compass and GPS system together, with the instruction to know how to use each before going out and to bring a physical map as a backup. That is a federal land agency’s standing advice, not an outdoor-shop upsell.

Where does GPS actually let you down?

Three places, and the US government publishes all of them.

Sky blockage. GPS.gov states the signal in space provides a worst-case pseudorange accuracy of 7.8 metres at 95 percent confidence, and that good single-frequency receivers attain horizontal accuracy of 2.168 metres or better 95 percent of the time. Then it adds the caveat that matters in the field: the accuracy users attain depends on factors outside the government’s control, including atmospheric effects, sky blockage and receiver quality. Canyon walls, dense canopy and steep terrain are sky blockage.

Cold. Garmin states plainly that all electronics have reduced battery performance at cold temperatures, gives its inReach handhelds a rating down to −20 °C, and advises carrying the device inside a jacket close to the body to extend battery life in cold. That is the manufacturer, in its own words, describing a limitation.

Standing still. This one surprises people. A GPS-derived heading is computed from movement — Garmin’s GPSMAP handhelds carry a setting that automatically switches from the electronic compass to a GPS compass once you are travelling at speed. Stop walking, and a unit without a working electronic compass cannot tell you which way you are facing. Electronic compasses in turn need periodic calibration.

And where does the compass let you down?

Two places, and one of them is genuinely dramatic.

Near the magnetic poles. NOAA defines blackout zones as regions around the north and south magnetic poles where the horizontal intensity of Earth’s field falls below 2000 nT, and states outright that compasses are not accurate there and should not be relied on for navigation. A caution zone runs from 2000 to 6000 nT where compasses should be used with care. High-latitude travellers plan around this; most people never encounter it, but it is the one place where “just carry a compass” is wrong advice.

Local anomalies. The World Magnetic Model describes the planetary field, not the rock beneath your feet. NOAA notes that local anomalies exceeding 10 degrees of declination exist, that 3 to 4 degree anomalies exist in limited areas, and that one area in Minnesota has a mapped anomalous 16 degrees east declination. The model explicitly does not represent the effects of the Earth’s crust and upper mantle.

To which add the obvious: a compass near a phone, a knife, a vehicle or a steel structure is reading that object, not the planet. At sea this becomes its own discipline — see why a boat compass doesn’t point north.

What is declination, and do you need to set it?

Declination is the angle between magnetic north and true north — NOAA’s own definition, positive east of true north and negative west. Your compass points at magnetic north; your map is drawn to true north; declination is the difference you have to apply.

It changes with location and over time. The authoritative source is the World Magnetic Model, jointly developed by NOAA’s National Centers for Environmental Information and the British Geological Survey, and a joint product of the US National Geospatial-Intelligence Agency and the UK’s Defence Geographic Centre. It is updated at least every five years; WMM2025 was released on 17 December 2024 and remains valid until late 2029. NOAA’s free declination calculator will give you the figure for a location and date, with declination accuracy generally within half a degree.

Do you need to set it? Suunto’s answer is more honest than most: in many parts of the world declination is so small that you do not need to take it into consideration in practical outdoor navigation — but in some places it is significant and must be accounted for. Look up your area rather than following a blanket rule in either direction.

If you do need it, buy a compass with adjustable declination, which Suunto describes as set once when you start navigating by turning the north arrow in the base of the capsule. It removes the arithmetic, and arithmetic in bad weather is how mistakes happen.

The buying detail nobody mentions

Compass needles are balanced for a magnetic zone. Silva explains it: Earth’s magnetic field differs between parts of the world, and most compasses are balanced for one of three zones — northern, equatorial or southern. Take a northern-balanced compass to the southern hemisphere and the needle drags or sticks.

Silva sells a global needle that works in all three zones. If you travel between hemispheres, that is the specification to look for, and almost nobody knows to ask.

Also worth knowing: Suunto’s baseplate compasses are rated −30 °C to +60 °C. There is no battery line in that spec, which is the entire point.

So what should you carry?

	Magnetic compass	GPS handheld
Power required	None	Battery, degraded by cold
Works under canopy or in canyon	Yes	Degraded by sky blockage
Works standing still	Yes	Only with a working electronic compass
Works near magnetic poles	No	Yes
Affected by nearby steel or magnets	Yes	No
Tells you where you are	No	Yes

That bottom row is the honest summary of why this is not really a competition. A compass tells you which way you are pointing; a GPS tells you where you are. They answer different questions, and a map is what connects them — which is why the Park Service lists all three.

Buy: a baseplate compass with adjustable declination from Silva or Suunto, a paper map of the area, and a Garmin handheld if you want position, tracking and — on the inReach models — the ability to call for help. Then learn the compass properly, because the failure mode of the backup you never practised is that you carry it and still get lost.