Navigation puzzle 11

We're going to have a look at a few more advanced techniques over the next few puzzles. Starting with transit lines this week.

This is a very useful way of pinpointing your location quite quickly. Imagine you had been walking east along the track to Llyn Bodlyn, and turned up the hill to the north. Along a path that was visible on the ground.

Rather than having kept a really close note of where you were on the ground, you ended up being a little uncertain of where you were on the wide saddle between Moelfre and Moelyblithcwn.

So, now you have an area of uncertainty that might look like this:

You manage to identify a couple of features that are nearly in line, in this case the trig point on the summit of Diffwys, and the boat house:

With a slight bit of movement along the path, you can now bring them perfectly in line:

Because of the shape of the ground, and the visible track, and the transit line between the trig point and the boat house, there is only one place that you can be on the ground - the point that the transit line intersects the path that leaves the track heading north and bends to the north east. This is also where an altimeter can be hugely beneficial and a technique I teach a lot for Mountain Marathon, it is so quick, so visual, but so pinpoint accurate that it is a tool to have in your pocket.

The puzzle for this week is to define these three locations by grid reference.

1. You are stood at an altitude of 450m and can only see the end of the field boundary between SH 7018 1289 and SH 7001 1283.

2. The peaks at SH 7827 2824 and SH 7943 2780 are in line, and at the same time the bends in the forest edge at SH 8076 2690 and SH 8074 2639 are in line.

3. You are looking south west at the airfield at SH 5699 2584 and can see straight down the SW runway - your altimeter says you're at 450m.