Navigation - Map Basics

I am going to concentrate on the essentials of a map that are used for navigation. Every map has a symbols chart and you can use this to recognise key features of a map. It is not worth trying to explain what every symbol means on every map. I am also going to focus on using a map with a compass.

For moutain navigation the most important details on the map are actually the contour lines. These brown lines that most people ignore will be one of the few things that you can use as aids for navigation regardless of the weather - even in fog you know whether you are going uphill or downhill!

• The Map Grid (1:50,000)
• Grid vs. Magnetic North
• Contour Lines
• Linear Features
• Spot Features (Landmarks)

The Map Grid

[This image can be clicked on to show more detail]

The map has on it a grid of blue lines which are called Eastings (X) and Northings (Y). The Eastings are vertical lines that are numbered from left to right. They are the X axis of the map. The Northings are horizontal lines that are numbered from bottom to top and are they Y axis of the map.

All map references are given in terms of this grid with the X and then the Y grid reference being given to form a 6 or 8 digit number. On a 1:50,000 map each square in the grid represents a 1Km x 1Km square and the diagonal is about 1.4Km.

For me to walk 1Km on good ground will take around 11 minutes and about twice that on bad ground. Of course for hilly ground I must add extra time.

The bottom line is that if I am planning a route and count the number of squares that I cross I can roughly work out how far I will be walking and the MINIMUM time that I should allow. There are all sorts of rules about this which I will talk about in route planning.

On the image above you can see the Eastings increasing from 81 to 90 and you can see one Northings line at 44.

Grid North vs. Magnetic North

There are two things that you need to know about Magnetic North.

1. It moves!!!
2. It is almost never the same as Grid North.

On the map image above you can see that both Grid North and Magnetic North are shown on the map edge. Even more interesting is the fact that it gives the variance at 5 degrees 30 minutes West of Grid North as of June 1985 with an annual change of 10 minutes East.

This map may not be 10 years old but the last reprint was 10 years ago. According to the map then, the Magnetic North variance will have reduced by 100 minutes (1 degree 40 minutes) and so the variance now between Grid and Magentic North will be about 4 degrees (which is two ticks on my compass).

Whenever you take a bearing from a map you will need to compensate for the difference between the compass and the map. This may seem tedious but it soon becomes automatic and you do not need to be perfect most of of the time - if you are accurate within a degree or two that will generally be OK.

The basic rule of thumb in making the correction is that if Magnetic North is to the left then you rotate the compass housing to the left (and so the bearing in degrees is increasing) and if it points to the right then you rotate the housing to the right (and so the bearing in degrees decreases).

In the UK currently (2007) most maps have a Magnetic North that is a few degrees west and so if I cannot remember (or see) what the correction should be for my particular map then adding 1 or 2 degrees to any bearing I take and it will be close enough over short distances ( < 1Km)

The single biggest thing that you can do to improve the accuracy of your navigation is simply this. Always compensate for the variance between Grid and Magentic North.

Contour Lines

Contour Lines are your invisible friends. Once you can make good use of these things you need never get lost again (probably). Even in dense fog you will still (by walking around) be able to tell what the ground is like simply because uphill feels easier than downhill even on a gentle slope.

It is very worthwhile to learn how the contour lines on a map relate to the real world. The simplest way to do this is to always have your map to hand and to compare what you can see on the map with what you can see around you. WIth practice you will be able to automatically relate one to the other.

Now let's look at some contour lines (and related information) in detail. To do this I have included a map extract of a non-descript peak called Fan Fawr which is in the Brecon Beacons.

Firstly, you can see that many of the brown lines have numbers written on them - 700 and 650. This is the height of that line in metres above sea level. On this map (at 1:50,000 scale) the thick contour lines represent 50M height increments and the thinner ones represent 10M increments.

Secondly, you can see that around Fan Fawr in some directions the contour lines are close together and in some directions they are far apart.

Now, let's assume that you are on the top of Fan Fawr in dense fog and want to find out firstly exactly where you are and secondly the safest way to descend. To do this we need to look in detail at the topography of Fan Fawr on the map and see what we can see.

On the top of Fan Fawr their are two main features that you could definitely identify even in fog. The first obvious feature is the Trig Point which will be a small concrete pillar about 1M tall.

The second feature is the spot height that is marked on the map. The spot height is the highest point on the peak. This one unfortunately is also near a cliff. Even so, if you are on the highest point that you can find and all directions lead down then there is a good chance that you are at this point.

To the east there are cliffs and to the north and north-east you can see places where the contour lines just disappear. Where you see this it is a sign that the ground is very steap or vertical whilst not actually being a cliff.

When contour lines are far apart the ground will be flat or slightly sloping and when they are close together the ground will be very steep. Generally if you can see all of the contour lines (on a 1:50,000) map then there is a good chance that you will be able to traverse the slope - but I cannot guarantee it.

So then, If I wanted to plan a route off the top and to the safety of the Storey Arms car park I must look in detail at the contour lines. The obvious safest direction off the top will be to head South for a few hundred metres and lose 100-150 metres of height. I can then drift east and then north.

The route I have marked out may seem complicated but in fact it is not. I do not need to be accurate. Basically all I would do is to head South for 300 or so metres (see measuring distance), go East for about the same amount and then chase the contour around the hill for 500 or so metres before heading down the slope towards the North-east.

This route includes a few features that I can use to check that I am on the right path. There are several streams that I must cross (and they or the dry remnants would be there at any time of the year) and there is also an area of ground that is flattish and has at it's centre either a small dent or a hillock. Either way, you should be able to see that once I am below the eastern cliffs almost any path down the hill will be safe.

Linear Features

A linear feature is simply one that is long and thin. It may be a river or a stream or a road or a path or even a cliff edge. The key thing is that a linear feature is relatively easy to find and relatively easy to hit.

There is one word of caution here. On many maps public bridleways and rights of way may be marked but on the ground their might not be an obvious path - either because the terrain (such as peat bog) does not allow it or because no-one has used that path in a long time. The other issue is that in some areas where there are sheep the sheep themselves may in fact leave little paths all over the place.

My planned route includes 3 streams which will act as linear features. I can estimate the distance between them and I know that if I cross 2 or 4 streams or they are not within 100M (or less) of where I expect them to be then I know that I have gone wrong.

A faster (and less safe) route would have been to head for the lake towards the east and then chase the edge of the forest (and then the river) to the north. This route would be much easier to navigate because the forest would be obvious when I hit it.

Point or Spot Features (Landmarks)

A spot feature is something that exists in a particular place and is easy to identify when you are there. Something like a Trig point or a junction of two paths or two streams or a bridge would be such a thing.

The key aspect of a spot feature is that it is easy to recognise when you are there. For example Trig points are quite rare as are bridges on a typical landscape. Junctions between paths are more common but could still be used.

The one thing to be wary of is where several similar spot features are together. It might be that in poor weather you do not know which one you are at. A classic case for this is Cairns (small piles of rocks). 10 or 20 years ago they used to be reliable as landscape features. However in the 90's it seemed to become fashionable for groups to build extra cairns to 'help' other walkers. Of course it made matters worse.