This section is mostly about what to do in the mist, but little on map and compass. Maps with contours are available on the web at 1:5000 scale from my Route Planner and at 1:25000 scale from StreetMap.co.uk. I reckon that no visibility was my lot on two thirds or more of the Munros, so some common sense as well as skill with map and compass are almost certainly required by someone in your party (even if you have an all powerful GPS). Every party must appoint a leader who is specifically tasked with ensuring the party stays on course. Otherwise you will surely get lost one day, suffering considerable indignity as well as additional unwanted climbing or missed objectives.
I know I walk about 1km in 15 minutes on typical Scottish mainland ridge terrain with average amount of up and down. By making allowances for fast and slow sections, I can guage my progress quite accurately from a known point even in very thick mist. I will also note times at tops and cols and the compass directions between them to double check later with the map if necessary when a ridge is fairly complex. (This was very useful between Carn Dearg (Newtonmore) and A'Chailleach.) Obviously position can be checked if the ridge dips below cloud level and a compass bearing can be obtained to a recognisable feature.
There is frequently evidence of a boundary fence or wall along a ridge between tops. Usually these can be followed until the map indicates that the boundary goes off in a different direction. (You need the 1:25000 maps for this detail.) Be careful not to follow them too far: any change in direction is usually obvious and the fence, wall or line of posts clearly leaves the ridge.
Munros generally have a very sizeable cairn at the true summit, one which is markedly larger than those on intermediate tops. There are usually small cairns on lesser tops, where a path splits, and particularly also where a path leaves the ridge to descend into a valley or down a side ridge. One or two tops have a number of cairns quite close together and it is unclear which is the summit in the mist: Buachaille Etive Mor is one of these, Beinn Teallach is another. My notes usually identify these.
Trig posts are very helpful in identifying one's position. They are usually, but not always, at the summit which is being ticked off, and their presence is always marked on maps. However, very few of the posts are still being used or maintained – most surveying is now from aerial photography. Consequently, a number have fallen over or lost their tops. In one or two rare cases the posts have disappeared without trace (such as on Ben Starav) – this may need to be taken into account if you're sure you've arrived but can't find the trig post.
Hills on map boundaries are a problem. I only took the wrong direction once, and that was crossing from A'Chailleach to Toman Coinich. The wind and rain were too strong to get out OS maps 19 and 20 and place them side by side to get an overall picture of the two mountains, so I relied on my memory. Oops – I collected a penalty of 250 extra feet of ascent! I partly relied on the rule of thumb, which is that the next top is further along the same ridge. This is normally correct, but not always. Unusually I should instead have retraced my steps. There are similar hiccups on the main ridge of Cruachan and the south Glen Shiel ridge. Make a note of such occurrences on your route plan.
I hardly used GPS. I'm not sure about its reliability when soaked in rain-hewn Scotland. Flat batteries are certainly a problem. I recall only one occasion where it would have been useful to me: in thick clag I turned up a ridge on Cruach Ardrain after descending about 100 yards short of where I should have been, and ended up on the top of an unexpected cliff. I like the challenge of having to use one's wits to find the right way. Then there is much more a sense of achievement when the goals are attained. Sat Nav would reduce that, although it could be encouraging to see how far one has progressed towards the next top. However, there is a clear advantage in using GPS in rain & high winds when maps become very unmanageable, especially on folds or edges.
If the cloud level is above one, then the clouds show what direction the wind is blowing. This can be quite different from wind direction on the hill where the ridges and valleys re-direct everything. Remember you can use the sun as a compass in good weather, and wind direction in mist and at night. If, for example, you ascend with the wind coming from your left, it should be coming from your right for a descent when re-tracing your steps (even if the topography has re-directed it). The normal prevailing wind is from the southwest and is never very cold, but particularly cold winds usually come from the east, northeast or north. Wind direction tends to change slowly, but often appreciably, over a whole day. It turns most quickly and sharply when a front arrives, and you should notice the rise or fall in temperature when that happens, perhaps also a change in precipitation characteristics. The arrival of a warm front typically causes a change from clear skies to heavy continuous rain to sporadic showers. I don't recall needing to use the sun as a compass except when driving around in towns and housing estates!
Copyright © 2007, 2012 & 2016 Colin Walter