Reading contours: ridges, valleys, saddles, steepness

Each contour line joins points of equal height. The height difference from one line to the next is called the contour interval and is stated in the map margin; on hiking maps, for example, 10 or 20 metres are common, but it varies from map to map. Often every fifth line is printed thicker (index contour) and carries a height value.

The spacing of the lines shows the steepness. When they bunch together, it is steep; when they are far apart, it is gentle. When they almost merge into a band, there is usually a steep wall or drop – many maps also show rock with special symbols or shading.

To tell uphill from downhill, use height values, summit points with heights, lakes and streams. Water always flows downhill. So where a stream cuts a V shape into the lines, the point of the V faces uphill, against the flow.

Valley or gully: the lines form a V or U whose point faces uphill. A stream often flows in it. Ridge or spur: the lines also form a V or U, but the point faces downhill. Ridges are often good, open lines for going up and down; gullies, by contrast, can be steep, wet and exposed to rockfall.

Saddle: the lowest point between two high points. On the map it looks like an hourglass or a butterfly – two sets of rings between which the lines bend outwards. Saddles are often natural crossings where paths lead from one valley to the next.

Knoll: a small closed ring, or several rings inside one another, shows a rise. Depression: closed rings with small tick marks pointing inwards mark a hollow without an outlet. Steep step: the lines bunch closely over a short distance and then spread out again.

Rock steps and drops lower than the contour interval can vanish completely between two contour lines. So a spot that looks even on the map can contain a step you cannot get down. Never assume the ground between two lines is even.

A convex slope – one that gets steeper and steeper further down – hides what lies below it. From above it looks harmless, and only when it is too late do you see the edge. So never descend steep sections 'blind'. If you cannot see how it continues, go back or look for a more open route.

The map also says nothing about whether a particular spot is passable – wet rock, loose scree or snow are not drawn in. Contour lines help you choose a safe route, but they do not replace your own eyes and your willingness to turn back.

Route choice: compare two possible routes by their line spacing. The one using gentler sections is usually safer and often faster, even if it looks longer on the map. Plan routes along gentler sections where possible, and over ridges rather than through gullies.

Finding your position: the landform often reveals more than paths, because paths change while ridges and valleys remain. Are you on a ridge, in a saddle or on a slope? With the compass you can even determine the slope's aspect: point it down the fall line of the slope you are standing on – the direction a ball would roll down – and look on the map for slopes that fall away in the same direction. That narrows down your position a lot.

Navigating without paths: in trackless terrain you can use landforms as handrails – up a ridge, along a valley floor, to a saddle. Experienced navigators often rely more on the terrain than on paths.

Take a map on a hike in familiar terrain and stop at distinctive places: where am I on the map right now? Am I standing on a ridge or in a hollow? Is it getting steeper or gentler ahead? Compare what you see with the lines.

At home you can build a simple model: shape a small mountain out of modelling clay and slice it with a thread into layers of equal thickness. Lay the slices on paper one after another and trace their edges – and you have your own contour map. Children immediately understand this way why close lines mean steep.