Understand Contours

Understand Contours – by Rob Johnson

If you can get your head around contours then your map reading will improve massively.

When map makers sit down with a blank piece of paper the first thing that they plot are the contour lines, they will always be accurate and they exist to represent the shape of the land. All of the other map detail is then placed on top and in relation to the contours.

In the UK our maps show contours at 10m intervals on OS maps and 15m on Harveys maps for the mountainous regions. Some low level areas will have 5m intervals. When you visit an area for the first time have a look at the heights shown on the contour lines and establish the gap between them. You will see that every 50 metres the contours are shown slightly darker, these are called index contours.

Learning to visualise the 3d landscape shown in contours takes some practice. In simple terms the closer the contours the steeper the ground. The diagram below demonstrates how they work:

You can see that a circle on the maps contours will represent a summit or pinnacle shape on the ground. Spurs and ridges are shown as fingers projecting further than the land around it whilst valleys and re-entrants are shown as scoops cutting into the land.

A really good way of getting your head around contours is to take some time to relate the map to the ground. Sit down for a short break and pick out features on the map to features on the ground as shown in the diagram below.

Once you have got your head around what the different shapes on the map mean on the ground you will be able to start navigating using the contours alone. This is especially useful in winter when the snow will cover much of the other information that is available to us on the maps.

To develop contour skills learn to anticipate the steepness of a slope by how close together the contours are, is it convex or concave, are there any crags/cliffs to negotiate? Try to teach others how they work, this is always a great way to test your knowledge aswell as transferring a potentially life saving skill.