Map Compass

A compass is only as useful as the map it sits on

The map compass range covers baseplate models made for reading a map, lensatic and prismatic military compasses built for taking sightings, and small carabiner or clip-on units meant as a rough direction check rather than a navigation tool. Choosing between them starts with one question: is the compass going to be laid flat on a paper map to set a bearing, or held up to the eye to shoot a bearing at a distant feature?

Which compass suits map reading?

A baseplate model, every time. The transparent plate sits directly on the map, the long edge lines up between two points, and the rotating housing transfers the bearing without any arithmetic. Roamer scales along the edges read grid references straight off the sheet. A sighting compass is more accurate at picking out a distant summit but awkward on paper, which is why plenty of walkers carry a baseplate for route work and treat anything else as a supplement. Either way, a map case and a compass belong in the same pocket as the rest of a survival kit.

Does magnetic declination matter in Britain?

It matters less here than in many places, and it changes over time. The angle between grid north and magnetic north is printed in the legend of Ordnance Survey sheets along with the year it was measured, so the value to use comes from the map in hand rather than from memory. Some compasses allow the offset to be set once with a small screw; on the rest it is applied mentally when converting between a grid bearing and a magnetic one.

What should be checked before buying a compass?

• Housing fluid: a liquid-damped capsule settles the needle quickly, and a bubble in the fluid indicates a failed seal.
• Baseplate scales: check that the printed scales match the map series being used, otherwise the roamers are decoration.
• Luminous markings: index line and north marker that glow after charging keep the compass readable at dusk without a light.
• Sighting method: a mirror or a lensatic window improves accuracy on distant targets; a plain baseplate is faster for close work.

Where should a compass be carried?

On a lanyard around the neck or clipped to a chest strap, never buried at the bottom of a pack, because a compass consulted only when lost is one that never gets used. Keep it away from phones, radios and steel buckles: magnetic fields deflect the needle and, held close for long enough, can reverse its polarity permanently. Route cards and map sections that need to stay dry belong in the lid pocket of a rucksack. That is usually the same pocket as the cordage used to pitch one of the camping tarps at the end of a leg.

Does a compass need maintenance?

Very little, and mostly it is about storage. Keep it out of direct heat, which expands the fluid and stresses the capsule seal, and store it flat rather than under load. Before any serious route, check the needle against a known direction, since a compass that has been sitting next to a speaker is the one that quietly points the wrong way.