Using terrain - Map to Ground
Sometimes it will be either impractical or simply too inconvenient and inflexible to travel on a strict bearing by dead reckoning. It is here that we use our sense of where we are on the map, and how this corresponds to the environment to move map-to-ground.
Map to ground
In its simplest sense, going map to ground is just moving according to a mental image of where you are on the map. This is a skill best practised. There are a few elements that must be considered.
Humans have a tendency to fit their surroundings into their mental picture of the world. How often have you heard folks vehemently argue that McDonalds is 'that way' pointing over your shoulder, when in fact it's 100m behind them. This is particularly relevant when all you have around you is a handful of very similarly-looking hills and re-entrants. First, you always have to be aware of which direction is north. Refer to your compass - often. Brotherton advocates a method he calls Radial arms in which you orientate yourself towards your attack point, and physically point or 'grab' at objects in Cardinal directions, distant features, or objects like the Sun to physically remember what direction is which. I can't say I do the full arm-flailing, but I realised when I read his description I do it automatically. Orientating where features are relative to your body is a good practise to get into.
Break up your navigation legs into mini-waypoints or stepping stones. I consider this in more detail with route planning. If your aim is to get to point B it may be easier to go in the general direction via Points A1, A2, and A3. At least if you do wander off in the wrong direction, you know the last point where you were sure you were so you can re-locate your position. I mentioned previously humans tend to want to verify what they think is the answer. To any trained scientists out there, this is anathema. We use a hypothesis-testing approach. Put simply, don't look just for the objects that should be there - look also for the things that shouldn't be there: For example All the hills and re-entrants seem to be in the right place, but the map doesn't show the bloody great mountain I see in front of me...; and predict what should be there: From here there should be a re-entrant going right to left. Oops... yes, where in fact instead of a re-entrant there is a hill. Something's wrong. When going map to ground you should be aware of your situation enough to not get caught like this, because you will be continually updating your position on both your mental and physical map.
Ridge and creekline travel
Ridges are convenient navigation routes. Once you do the hard work and get up onto high ground, ridges are generally easy to follow. Vegetation is typically less dense compared to creeklines, and animals will have contributed to clearing tracks on ridges. For you hunters out there, ridge and creekline searches are a good way of locating prey. Having a high viewpoint helps you maintain a clear picture of reference points around. Ridges conveniently lead to spot heights, so it is relatively easy to plan a route.
Creeklines present a bit more of a problem. Following a large river valley is pretty easy - especially when you have clear view of the high points around you. Large rivers can be convenient navigation markers. However following creek lines or re-entrants can be tricky. Creek junctions can be indistinct in flat areas. Often the surrounding terrain is too flat to register as a spot height on the map. Additionally it is easy to start heading up the wrong line in areas with limited visibility, particularly in very convoluted ground with multiple similar-looking re-entrants. Also, creek lines by their damp and protected nature are typically more heavily vegetated.
As the name implies, contouring is following a contour line. It has a few good things going for it. First, walking at the same altitude is easier on the legs than crashing up hills and down scree slopes. Second, in very convoluted territory it is simply easier to focus on a far point and sinusoidally wind your way to it rather than break it up into short distance/direction legs.
There are some pitfalls to be aware of.
First, you need to disciplined during travel. Just as humans (and animals for that matter) tend to walk on one side of obstacles, leading to drift, humans tend to drift downhill. Why? Because it's easier. This can be partly offset by doing what you should do when trying to walk in a straight line - alternate going uphill and downhill of any small obstacle on the path. Another trick that is useful is to use the horizon as a reference. From your current position, hold your arm outstretched at eye level to the horizon, and draw an imaginary horizon to the direction of travel. Pick a convenient point where your arm intersects the direction of travel - this is your aiming point.
Second, keep a close eye on your ultimate direction of travel. As you meander around the contour, your local direction of travel will vary widely. But if you have a general direction in your mind - particularly with an aiming point in the distance - your chances of ending up 180° from your intended direction are reduced. Arcs or circles are notoriously difficult to navigate on.
Third, be particularly aware of distance travelled. If you have picked a meandering contour course with no clear aiming point it is possible to get confused about whether you have gone too far, or far enough to see any catch point. This is more a problem of inducing uncertainty into your confidence of where you are. I got caught by this on a patrol when I was contouring around a set of features and my catch point wasn't yet evident. When I hit the 'where the hell exactly am I?' stage, a quick confab with my check pacer and check nav confirmed we simply hadn't gone far enough. The contour distance is far more than you would expect from a straight line.
Example route: Map to ground
Lets look at an example to get an idea of the mindset when planning and executing a map-to-ground route. First things first - I still make a Nav Data Sheet as if I were doing the route by dead reckoning, with the different legs reflecting major changes in direction. This way, I always have a fallback if bad weather moves in and I can't see, or someone in the party needs to backtrack to get help to recover my lifeless body from under a stray meteorite or whatever.
I want to get from turo Punco spot height 2493 - from where I was blissfully contemplating my existence and plotting to take over the world - to spot height 2511 from where a friend of mine phoned to let me know he has a new parapent he wants to test from Pic Negre, and he wants me to fly his old one down as he tests the new one. Fair enough.
The dead reckoning route is 300° for 3475m. The route wouldn't be hard, but there are a few ups and downs I could avoid, and a bit of a steep climb at the end. I'm going to take the scenic route. First I sketch out a plan and do a map reconnaissance. I look at convenient features. Spurs are easier to navigate, but streams are useful navigation handrails - but the streams here tend to run into steep valleys, so I only want to stay with them on the flat. I will make a nav data sheet - but the route will be pretty straight forward without it. I trace out the route and measure it - about 4100m. That's not going to kill me. All set to go...
a) First make sure my map is up the right way. There's nothing more embarrassing than starting off 180° to the intended direction. The first leg will be about 280° following the easy ground until I get to the creek line. If I'm loosely on this bearing then the creek junction (my collecting feature) will be on my left, so I can make my way to that. Effectively the creek is a small handrail for a bit.
b) At the junction, Spot Height 2612 should be at 45°. However I will be at 1980m, possibly with some forest in the way. The spot height may not be visible or distinct, however the slope/spurline leading to SH 2612 will run approximately 40-45°. There are no other creek junctions around, so this is right.
c) From the junction I go straight up the gentle spur at about 325° for 300m. Here, the ground will flatten out and the vegetation will thin to a clearing about 100m in front of me.
d) I veer left and follow what should be the 2150 contour.
e) As my bearing starts to come eastward to approach 325° again, a large spur leading to spot height 2612 will appear and I will hit some clearings. If my bearing starts going North, I've walked too far along the contour. I continue to the creek line. At the creek SH 2612 should be at 25°. While there's no intervening vegetation, the height might not be distinct, but as long as the even upward slope is perpendicular to 25° it's looking good.
f) Here I go due West for about 200m until I hit the spur line. This spur should be pretty obvious, so I hang a right along it. The spur should steep off more sharply to the right. As I go up the spur, if SH 2612 wasn't visible before, it will become visible now on my right.
g) I now reach 2511. I know this because I take a bearing of 25° to SH 2612, and I can see the 2487 knoll NNW about 200m across the saddle. Also, my smirking friend is there and tells me he actually parapented in from Pic Negre already, and just wanted company to walk back up again. Utter, utter b******!
I consider this in route planning. Whether going map to ground or dead reckoning - and in actual fact it's generally a combination of both - developing a narrative of the planned and actual journey is essential to maintaining awareness of where you probably are, and certainly where you have been. This will greatly minimise your chances of getting geographically challenged.
Geology, fickle beast that it is, can play tricks on us by making features that look kind of similar to each other, kind of close together. In this example, if we are at all uncertain about or start point from this pretty featureless slope with no clear features, and intend to go down a spurline - there is a very real chance we could end up on the wrong one. If visibility is limited, we will have a real problem until we have gone at least 500m or so and new topographic features we encounter start to indicate something is wrong.
This is complicated by the fact that the similar features could be in front of, behind, or to the side of the one we think we are navigating to. Often this is not immediately apparent because of error in taking bearings. However, as we get closer we realise the two features that were nearly in line with each other are in fact quite different. Oops, we've been following a bearing to the wrong thing. In mountains the 'one in front of the other' problem can be particularly tricky. Measuring relative heights of features different distances away requires a bit of mental perspective estimation. In clear conditions a line of peaks leading away from us could look like a single peak with a few crags around it. Indeed the peak we planned to take a bearing to may not be visible because of those in front - a problem of intervisibility.
There are two things we need to do to avoid this. First, be aware of the map! Just because a peak is labeled on the map does not mean that it is the obvious one in front of you. Don't assume - be sure and consider alternative explanations for what you see. Second, when on the move pay attention to other features around you. Develop catching points, and anticipate which other features should be at what angle from you at which point along the leg.