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Understanding Contour Lines – Tip #54

By 29th November 2020February 5th, 2021Navigation, Resources, Tips

Understanding contour lines

These little tips should help improve your understanding of contour lines and how to interpret them. One of the most important navigational skills is the ability to visualise the two-dimensional contour lines in ‘3-D’. This is a major topic on our mountain navigation courses.

Estimated reading time: 3 minutes

A 3-D model helping to understand the contour lines on Tryfan and the Ogwen Valley in Snowdonia

The first stumbling block that many people have, however, is in trying to decipher which way is uphill. For example, is a series of concentric rings of contours representing a summit – or a deep hole? Or, on an open area with many parallel contours, where is the top and bottom of the slope? And what about the V-shapes or U-shapes – when contours bend to form a ‘V’, are they showing a valley or a ridge?

It’s a complicated picture and this skill takes time to practice and master. However, here are three simple clues to look for that will give you a nudge in the right direction. These tips should help you understand and interpret contour lines much more quickly.

Numbering sequence

This is the easy one. Sometimes there are a set of contours where all the contour numbers are visible (for example 50, 100, 150, etc). It’s obvious that the top of the slope is near the 150m contour and the bottom is near the 50m contour. You can trace these contour lines around the hillside. You can then identify the top and bottom of the slope in an area where no numbers are shown.

Number orientation

However, sometimes the map maker is short of space and will choose to print to just one contour number in a whole area, meaning that you can’t use the obvious sequence technique. But all is not lost. The number will be printed in such a way that it is printed “the  right way up” on the hillside. If I type an imaginary contour line here “—— 350——-” this would indicate that the top of the page is higher up the slope than the bottom of the page. Just try to imagine which way the numbers would be facing if they were actually real features printed on the ground – the top of the numbers is uphill.


We all know that water flows downhill – obviously. So therefore, every water symbol on the map (such as a small stream) must be a lower point than anything else in its immediate vicinity. So if the map shows two parallel streams, then the terrain between the streams must be higher. This simple fact will help you identify which of the V-shapes are valleys or ridges separating the valleys. Try this – place your hand palm-down and spread out the fingers of your hand.  Identify the ridges (fingers) and the valleys between them (the spaces), as they run away from the top of your hand (the summit). Where would contour lines be drawn on your fingers? Which way do the V-shaped contours point to represent a valley and a ridge?