Why contours matter more than grid lines

Grid lines tell you where you are. Contours tell you what the ground is doing. On a British hill, a straight line on the map can mean a pleasant amble or a knee-deep scramble through heather and scree. The difference is in the contour lines. Learning to read them is the single most useful skill for planning a fell walk that matches your experience and energy levels. It keeps you safe, and it makes the day more enjoyable.

The three key patterns: spacing, shape, and direction

Contours are imaginary lines joining points of equal height. The interval – the vertical gap between them – is usually 10 metres on a 1:50,000 map and 5 or 10 metres on a 1:25,000 map. Always check the legend. Once you know the interval, you can read three things at a glance.

• Spacing: Lines close together mean steep ground. Lines far apart mean gentle ground. Evenly spaced lines mean a steady, consistent slope.
• Shape: A V or U shape pointing uphill indicates a valley, re-entrant or cwm. The same shape pointing downhill indicates a spur or ridge.
• Direction: The way the V points tells you which way water would flow. That is the way the ground falls.

Put those three together and the map starts to look like a 3D landscape. You can see where the steep bits are, where the easy ground lies, and where a ridge gives you a natural handrail.

Reading ridges, valleys and cwms on British hills

On a British hill, ridges are your friends. They offer firm ground, good views, and a simple navigation line. On the map, a ridge appears as a series of contours that form a U or V pointing downhill, with ground falling away on both sides. The crest is the highest ground between the V shapes. If you follow that crest, you stay on the ridge.

Valleys are the opposite. A V pointing uphill shows a valley or re-entrant. The deeper the V and the closer the contours, the steeper the sides. In the Lake District, Snowdonia and the Scottish Highlands, you will often see a horseshoe of tight contours – that is a cwm or corrie, a steep-sided bowl carved by ice. They are dramatic, but the headwalls are often loose and pathless. If you are not confident on steep, trackless ground, plan to skirt around the rim rather than climb straight up the middle.

Watch for contour lines that bunch at the top of a slope. That is a convex slope – it steepens as you descend, which can be dangerous if you are tired or the ground is wet. Lines that bunch at the bottom give a concave slope: steep at first, then easing. Both are useful to know before you commit.

Matching steepness to your experience and energy

Not all height gain is equal. A route with 600 metres of ascent spread over 12 kilometres is very different from 600 metres crammed into 4 kilometres. Contours let you estimate both steepness and effort before you leave the house.

For a rough guide, use Naismith's rule: allow one hour for every 5 kilometres on the flat, plus one minute for every 10 metres of ascent. On steep ground, add extra time. If the contours cross many lines in a short distance, you will be moving slowly – perhaps 1 kilometre per hour or less. That matters on a short winter day.

Match the route to your group. If you are new to fell walking, choose routes where the contours are widely spaced or follow a ridge. Avoid direct ascents where the contour lines are packed tight. If you are fit and experienced, a steep pull can be fine, but always have a plan B.

Energy levels drop during the day. A route that looks fine on paper can feel brutal after five hours. Contours help you build in options. If you can see a lower-level return that follows a valley, you have a bail-out. If every alternative crosses tight contours, you are committed. Plan accordingly.

A practical routine for planning a safer route

Next time you plan a fell walk, try this routine. It takes five minutes and can transform your day.

• Check the contour interval. Know whether each line is 5, 10 or 15 metres. Write it down if it helps.
• Trace your intended line. Count how many contours you cross. That is your total ascent. Count them again on the descent.
• Identify steep sections. Where are the lines closest together? Are they on your route? Can you avoid them?
• Find handrails. Ridges, streams, walls and path junctions. A ridge shown by a V pointing downhill is a gift – use it.
• Plan escape routes. Look for a valley or a gentle spur that leads you down safely if the weather turns or energy fades.
• Estimate time. Use Naismith's rule, then add 25% for a group, bad ground, or poor weather.

Finally, remember that contours are only part of the picture. Paths, crags, bogs and vegetation all matter. But if you can read the contours, you will never be surprised by a slope again. You will choose routes that suit your legs and your head, and you will enjoy the British hills all the more for it.