Index of Information

Compass and map
 

The importance of being able to read a map and compass proficiently can not be highlighted enough. I mean lets face it, you don't want to be one of those people who have to be rescued by the Mountain Rescue team because they got lost when a little mist came down. Or on a more sombre note, you don't want to be one of those people who are less fortunate and are not rescued in time.

The long and short of it is that the mountains in Scotland can kill, so we shouldn't underestimate them or take them lightly. All it takes is a short time to learn those basics and enhance your safety on the mountains..... so how much do you know?


Basic Map Info.

The grid lines on Ordnance Survey maps are used to:
1. Determine the grid reference of a location
2. Find a location from to its grid reference.

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Reading and Using Grid References

Grid references are 6 digits long. The numbers are two batches of three, where the first two digits of the batch indicate the "box" the landmark falls in. The third digit indicates the location of it within the box. For example, the 0 in 670 would be exactly on the grid line 67 and where 675 would be half way from grid line 67 to grid line 68.

Grid lines

On Ordnance Survey maps are 1km apart regardless of the scale of the map.

Northings - the figures are read vertically bottom to top up the map and the lines that join these figures run horizontally left to right
Eastings - the figures are read horizontally left to right across the map and the lines that join these figures run vertically top to bottom.

Grid refs. should be read from the map in the following order:

  1. Eastings (i.e. across the map east to west)
  2. Northings (i.e. down the map north to south

N.B. Eastings; Northings = E then N (alphabetical order)

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Compass navigation

A basic Silva Compass will provide you will all the functions you are likely to need.

  1. Try and guess the bearing you are about to calculate.
    • Remember the Cardinal Points/4 Quadrants of your compass - North 0 degrees; East 90 degrees; South 180 degrees; West 270 degrees and North 360 degrees This gives you a cross check.
    • Alarm bells should begin to ring when your guess is way out (usually about 180 degrees!) from the bearing you have worked out.
  2. Lay out map and compass on top
  3. Place edge of compass along line A - B.(You are walking from A to B - Direction of Travel Arrow points this way)

    [Mistake No 1 - You have the compass back to front i.e. Going from B to A]

  4. Set Orienting Arrow (big, black/red depending on your compass type which lines up with North/0 degrees on your compass dial) to North (top) of map.
  5. Line up accurately with grid lines by turning dial.(Use orienting/parallel lines).

    [Mistake No 2 - lining up the orienting lines with North on your dial pointing to the left right or bottom of your map; MUST be to top]

  6. Read grid bearing against your direction of travel arrow/ line, turn dial anti-clockwise to add 5o (five degrees - 1 mark = 2 degrees) to give magnetic bearing.
  7. Lay aside map; swing compass in hand until red magnetic needle and black/red orienting arrow are together.
  8. Walk in direction of arrow at front of compass. (Direction of Travel Arrow)

For Quick orientation

  1. Lay out map and compass on top
  2. Set the bearing on the compass to north
  3. Line the edge of the compass base plate and the orienting lines on the compass with the eastings (gridlines running east to west)
  4. Turn the map (and yourself) until the red end of the arrow points north.
  5. You are now facing north and the top of the map is now pointing north.

Using a feature on the ground to get a bearing

Point the compass's "direction of travel" arrow at a feature on the ground (i.e. a house in the distance). Turn the housing until the red "N" lines up with the rotating arrow.

You can travel along this bearing using the compass or you can convert it to a map bearing to plot a location by:

  1. Subtract 5o (as it is Mag to Grid - GET RID - see below for more information)
  2. Lay the compass on the map until the orienting lines are parallel to the map eastings and the base plate is running through your current position on the map.

 

Things to Watch Out For

  • Metal objects can cause the needle to deviate from north. Stand clear of metal objects.
  • Always hold the compass flat - it allows the needle to move round freely
  • Take care of your compass - a damaged compass could become inaccurate
  • Always use an up to date map as old maps may be missing information or may even detail landmarks that are no longer there.
  • Replace your compass if it develops a large air bubble. Work on the safe side!!

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Mountain Safety and Sense

  • Always tell someone your route for the day - even if it is a simple route. The make sure you stick to the route you planned!
  • Make sure you are properly equiped and fit and capable enough to complete your chosen route with ease.

A list of mountain safety recommendations:

  • DO wear good walking boots and wear or carry waterproof jacket and trousers
  • DO carry a map and compass and know how to use them
  • DO carry a whistle and know the international distress signal
  • DO prepare a route card and leave a note of your proposed route
  • DO carry enough food and drink for more than a full day on the hills
  • DO carry a survival bag and spare clothing
  • DO carry and ice axe, crampons and torch in winter and be proficient in their use
  • DON’T go to the hills alone if you are inexperienced
  • DON’T overestimate your own abilities
  • DON’T underestimate the variability of Scottish Mountain Weather at any time of the year


True, Grid and Magnetic North

True North and south are located at the geographic poles.
Grid North is the direction to which all of the Ordanance Survey maps are orientated. All the map bearings that are taken use grid north.
Magnetic North is the direction that a compass points to. In the UK this is approximately 5o west of grid north.

The difference between grid and magnetic north is referred to as the magnetic variation and must be taken into account when translating bearings from or onto maps.

So how do you deal with magnetic variation?

Because the information we take from a map is based on grid bearings and the information from a compass is based on magnetic bearings, when we move from one format to the other we must take this into account. This is simply by either the subtraction or addition of the magnetic variation (5o) to convert the bearing.


One system is simply:

Grid to mag(netic) - ADD (i.e. add to the grid bearing)
Mag to grid - GET RID (i.e. subtract from the magnetic bearing)

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