Virtual course: Control #3

Judging contour lines is perhaps the most important skill required for advanced trail orienteering. Here is a simple example.

The photograph shows a small spur. The lower flag is at the foot of the spur. The upper flag is near the top of the spur and the centre of the circle on the map is above the contour line and within the spur shape. Flag A clearly matches the description of ‘spur, upper part’ and the centre of the circle on the
map.

Solution: Flag A.

However, this example is not as elementary as it first appears. Where does the contour line run across the spur on the ground? Along the foot of the spur or at some intermediate height? Had another flag been positioned between the existing pair and the description changed to just ‘spur’, the problem would
have been much more difficult. To arrive at a solution, it would have been necessary to judge the line of the contour with some precision. How is this done? The below advanced tip explains.

Advanced tip

There are two ways in which contours may be judged across the terrain. The first is that, if there is good variation in the shape of the contour, it might be possible to estimate its position by eye, from size and
depth of view. This skill is achieved through repeated practice. The second method may be used if the contour runs through or by a mapped feature, such as the boulder in the above example. Using the feature as a starting point, the contour may be traced across the terrain. This requires a good sense of
the horizontal.