Plotting and planning a Course

Taking a bearing from a map

By now you will have read and understood basic map skills and basic compass skills. We can now apply these skills to identify a bearing that we will follow.

Let's assume for now that I am on the path following the cliff on the lower right corner of the map. I am now somewhat tired and losing daylight and so I want to find a quick safe route back to the main road (top left). Let's also assume that it is a little foggy (a sure thing in winter).

The obvious safe route down is to walk down the centre of Gwaun Nant Ddu and pass through the gap in the forest. [In practice I would aim for one or other of the forest edges and walk down but that is more advanced].

1. What I have done is place the compass onto the map and used one of the parallel lines on the compass base plate. I have aligned the parallel line so that it joins up the point where I am standing (On Graig Fan Ddu) and points to the middle of the forest on the top left. (The base-plate line that I am using is the one attached to the 1:63,000 scale, but any of the long parallel lines or the compass base-plate edge would be ideal.

2. Next I align the black and red lines on the compass housing so that they are parallel to the grid lines on the map with the red sections towards the North and the black sections towards the South.

The number one mistake that I will make when tired is that I will align these markings with the wrong grid lines and thus produce a bearing that is wrong. Always check that the base-plate lines are correctly aligned with the map grid lines.

On the compass you should be able to see that the comapss housing is showing a bearing of about 208 degrees.

Here it is in close-up. You can see that the thin line underneath the compass housing is at 208 degrees (roughly) and that this line is in line with the direction-of-travel arrow (compass basics).

The final thing that we need to do is to adjust for magnetic north which on this particular map in 2007 is offset by about 4 degrees (map basics)

I now have a compass bearing that I can follow. All I now need to do is to work out how far I need to walk...

Estimating distance from a map

For this particular route I have been forced into a situation where the only landmarks I have are the forests (top left) and my starting point.

The distance I want to travel is more than 1Km and so I cannot do what I would normally do and use the 1:50,000 scale on the base-plate. Instead I am using the metric ruler. This gives me a measurement of 72mm which when halved (1:50,000) gives me a distance of 3.5Km.

The height at my start is 740m and at the end by the forest is about 500m - a drop of 220m. If I was walking uphill then following Naismith's rule of allowing 1 minute for every 10 metres I would need to allow an extra 22 minutes. Since I am going downhill it will be faster but I still need to make allowances for the extra distance that a slope implies and so I am going to estimate an additional 11 minutes.

Putting it all together - walking the walk

The route down has been chosen so that I will take advantage of the local terrain in order that I can stay on track - even if the ground is rough underfoot. As you can see from the map Gwaun Nant Ddu has a gentle slope down and relatively steep sides. If I drift too far to either the left or the right on my descent then the ground will become suddenly steeper and I will know that I have gone adrift and can adjust.

I have chosen to aim for the forest on the top left rather than the centre. I am assuming that my navigation will not be perfect and that I may drift a little. The forest is a nice big linear feature and should be relatively easy to hit. No matter where I hit it I know that all I need to do is follow the edge of the forest down the hill and I will reach my desired point.

Finally, I am about ready to follow the compass bearing and walk down the hill. From my personal knowledge of how I walk (see calibration) I know that I will walk 1km in 11 minutes. This gives me a total estimated walking time of (3.5 * 11) + 11 = 49.5 minutes which is quite long for a single leg of a journey.

To measure this I will use either a stop-watch or a countdown timer (which was already set to 11 minutes) with my ranger beads to count off each 1Km of the watch.

After about 40 or so minutes I would expect that the forest would be nearby and I would mentally start to be more alert for treas appearing in the fog. After 60 minutes if I still had not seen any forest I would need to consider whether or not I have gone astray. On the route I have chosen if I was still walking down a gentle slope and walking roughly SSW I would probably assume that I was just walking more slowly than normal.

Of course if I had a GPS with me I would switch it on and check - but that's not so much fun is it? ;-)

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