Somewhere on a hillside, the wind is doing its best to fold your map in half. That is the moment a paper map earns its place in your pack: no battery, no signal, and it shows the whole valley at once. Reading it well is not a dark art. Four things do most of the work — the grid, the contours, the rights of way, and the habit of checking the ground against the paper. Get those right and you will plan better walks, walk them with more confidence, and know exactly what to say if you ever need to call for help.

Grid references: two letters, then the numbers

Every Ordnance Survey map of Great Britain sits inside a national grid. The country is divided into 100 km squares, each labelled with two letters — SU, NY, NN, TQ and so on. Those letters are printed at the corners of the map and repeated inside it, so you can always work out which square you are standing in.

Within each square, the grid lines create 1 km boxes. A grid reference reads eastings first, then northings: along the corridor, then up the stairs. Find the vertical line to the west (left) of your point, then the horizontal line to the south (below) it.

• Four figures — SU 123 456 — identifies a 1 km square. Fine for "somewhere in this field".
• Six figures — SU 1234 4567 — narrows it to 100 m. This is the standard for telling a friend where you have parked, or for passing a location to mountain rescue.
• Eight figures — accurate to about 10 m, used for pinpointing a specific gate, crag or bothy.

To read a six-figure reference, split each half: the first two digits are whole kilometres east, the third is tenths of a kilometre east. Estimate it by eye, or use the roamer scale printed on the baseplate of most compasses. The OS Locate app converts your phone's position into a grid reference and works offline, which is handy — but keep the paper version as your main source.

Contour lines: what the ground is actually doing

Contours join points of equal height. On OS Explorer maps at 1:25,000 the interval is usually 10 m; on Landranger maps at 1:50,000 it is often 50 m. Every so often a line is numbered or drawn thicker, so you can count your way up a slope instead of guessing.

The spacing is the message. Lines packed tightly together mean steep ground — a cluster almost touching is a crag or a sharp pull. Lines spread wide mean gentle gradients, the sort you barely notice until you check the map. A summit appears as a closed ring, often with a spot height or a triangulation pillar marked beside it.

Two shapes are worth learning early. In a valley, contours form a V pointing uphill, with the stream running through the point of the V. A ridge or spur pushes out from higher ground as a series of finger-like folds, and these are often the pleasantest lines to walk: steady climbing, better drainage, fewer boggy patches. Ring contours with small inward-pointing ticks (hachures) mark hollows and depressions, which collect water in wet weather.

Rights of way: the lines you are allowed to walk

This is where people get caught out. A path on the map is not automatically a right. The coloured dashes mark public rights of way, and each type carries different legal rights. On OS Explorer maps, footpaths generally appear as short yellow-orange dashes, bridleways as longer green dashes, and byways with cross ticks — but styles vary between scales and editions, so read the legend on your own map.

• Public footpath — walking only.
• Public bridleway — walking, horse riding and cycling. Cyclists must give way to walkers and riders.
• Restricted byway — walking, horse riding, cycling and non-motorised vehicles such as horse-drawn carts.
• Byway open to all traffic — legally open to vehicles, though in practice many are only passable on foot, bike or horse.
• Permissive path — not a right, but the landowner's permission, sometimes closed on certain days.

The line tells you about access, not surface. A footpath can be ankle-deep in February. In England and Wales, open access land — mountain, moor, heath and registered common land — is shown as a pale orange wash on Explorer maps, and you may roam on foot there subject to local restrictions. In Scotland, the Scottish Outdoor Access Code sets out a right of responsible access over most land, whatever the map colour shows.

On the ground, look for waymark discs and arrows on gates and posts. In many counties yellow marks a footpath, blue a bridleway and red a byway. If a sign on the ground contradicts your map — a diversion order, a temporary closure — the sign wins.

A handful of symbols worth knowing

• Water — streams and rivers in blue, marsh in tufted blue symbols. Marsh symbols are a good clue to where boots will sink.
• Woodland and scrub — green shading. Shelter and shade, though the path along a wood's edge is often the muddiest.
• Gates, stiles and footbridges — small marks that tell you the path is waymarked and maintained at that point.
• Crags, scree and rocky ground — fine dot patterns and black hachures; treat as a warning on a wet day.
• Useful stops — parking, picnic sites, pubs, cafés, campsites and viewpoints are all marked.

Putting it together on a route

1. Fold the map so the area you need is visible and the grid letters are still in view.
2. Set the map: turn it until features on the ground line up with the symbols on the paper, or use a compass to align grid north.
3. Trace your route with a finger and note the distance and total climb. On Explorer maps, 4 cm equals 1 km.
4. Estimate time. A rough rule for an average group is 4 km per hour on the flat, plus about a minute for every 10 m of ascent. Add time for mud, stiles, photo stops and tired legs.
5. Mark two or three escape routes — a track, a valley, a road — and note the landmarks you will pass, such as a wall corner or a stream crossing.
6. Write down the grid references for your start, key points and finish.

Before you set offPhoto: Nataliya Vaitkevich / Pexels