By: Blonde Two
Most people who learn to navigate with a map and compass, at some point have to do a bit of triangulation. The correct term for it is resection and it involves a compass, a map, three known landmarks and a Blonde who isn’t quite sure where she is.
I used to be quite slick at a bit of the old resection work – probably because I used to spend quite a lot of my walking time not quite knowing where I was. These days I don’t practise it too much which must, I guess mean that the general tendency is for me to know where I am. We are talking, of course, about out in the hills now – I frequently don’t know where I am in town or when I am driving the Blonde Mobile.
I prefer to call it triangulation because if you do it properly, you end up with a 100m triangle on your map with a big sign saying “You Are Here!” (ok so I imagined the sign). If you do it wrong, you end up with a load of confusing lines across your map that mean nothing at all. It goes a bit like this;
1. Find three tall things in the distance that you can definitely identify (I would like to point out here that if you are already lost, this may seem tricky).
2. Point your compass direction of travel arrow at one of your known things and set a (back) bearing.
3. Do the magnetic deviation thing if you want to (remember to reverse it – “world to grid = get rid”).
4. Lay your compass onto your map and line the lines on it up with the North South lines on your map. This is the tricky bit – because you are reversing the usual map-to-world process, you need to remember to line your compass up in the reverse direction. You can use a protractor for this bit but I never have one handy.
5. Draw a line on your map (obviously not the floor!) between the known point and where you might be.
6. Repeat this for all three points.
7. Either – a) Look at the nice triangle you have drawn on your map and think “I know where I am now.” or b) Look at the mess of lines on your map and get your GPS out.
So give it a go next time you are out in the hills. A few warnings though: a) Don’t get lost on purpose just to try it out. b) It isn’t a very helpful method when the mist is down (unless you happen to know the precise location of three nearby cow pats on your map). c) Try not to think about it too much – in my experience, a little bit less understanding can be a very good thing.
Tomorrow, I am going to tell you about our Dartmoor Rescue friends and their alternative method of triangulation!