Map Reading & Navigation – Part 4

Before we can start to plan a route, it is important that we understand how to calculate the timings of each leg of our walk.  This can be done by using Naismith’s Rule.

Naismith’s Rule

Naismith’s Rules was created as a means of using distance and ascent to calculate the time taken to complete a walk.  In its most basic form, his simple rule was to

allow 15 minutes for every 1Km forward, plus 10 minutes for every 100m of ascent.

Naismith's_rule.svg

The reality of Naismith’s Rule is that it is dependent on:

  • Fitness levels
  • Speed of the slowest person
  • Size of the group – larger groups tend to travel more slowly
  • The terrain – rocky, heather, boggy, deep undergrowth etc can all slow you down
  • Steepness of the slope?
  • Wind speed and direction
  • Weight being carried
  • plus, many many more factors

For a slower walker then set a 3km pace, or 1km every 20 mins.

Example: I am heading up Pen-y-Fan at a rate of 4km/hr and 600m/hr.  The route is 3.14km long and the total climb (ascent) is 494m.

map

Horizontal time  =  dist ÷ rate × 60mins = 3.14 / 4 x 60 = 47 minutes

Vertical time  =  height ÷ rate × 60mins = 494 / 600 x 60 = 49 minutes

∴ Total time  =  47 + 49 = 96 minutes or 1hr 36mins

For a more detailed description go my blog Naismith’s Rule

Route Card

One final thing to consider before planning a route is the Route Card.  This is a piece of paper on which we write the details of the route we are taking showing the Bearings, Distance, Climb/Descent and Time Taken for each leg of the route.

There are many different examples of the Route Card and a quick search online will show you what is available.  Some ask for details about the members of the party, the equipment you are carrying plus details of start and finish points and over all timings.  This is used primarily as a record of your intentions, left with a responsible person.

For the purposes of this article I am using a simple Route Card

routecard

Plan A Route

The purpose of route planning is to come up with a detailed plan of the intended route for the days walk.  It should provide enough information, that anyone not involved in the planning should be able to pick it up and walk the route as intended.

The amount of detail one needs to go to is dictated by the terrain across which you wish to walk.  Remote mountainous areas will require a greater degree of planning than a walk around a local park.

Example: I have taken a random area and drawn a route that takes me from the start point, via three waypoints to the final destination at a Sheepfold.

drawn route

Using a compass, I have measured the magnetic bearing for each leg and its distance.  Using the contour lines, I have estimated the amount of climb/descent for each leg.  Finally, using Naismith’s Rule, I have calculated the time to complete each leg.

I have annotated the start and finish with an OS Grid Reference and simple description for each waypoint and added notes about each leg highlighting terrain, hazards, obstacles and navigation fix points.

route sheet completed

Exercise: It is now your turn.  Select a map and chose an area. Draw your route as a series of straight lines, then complete a route card.  Take this route card, with the map and compass, and go out and walk the route.

The more you practice this the easier it will become.  Start off with short routes, like the one in my example, then increase the length and complexity as you become more confident.

There is one other thing to consider when route planning. Though it’s real significance becomes apparent when briefing each leg to your party.

The Five D’s

Every time you plan or navigate from one waypoint to another, you need to consider the 5 D’s

Direction – This could be simply east, north-west or a specific magnetic bearing.

Distance – How far do you have to walk? This could be to the next waypoint or until the next feature.

Duration – How long should this leg take? Use this as a gross error check to see whether a mistake has been made in transit.

Description – What should you be looking out for en-route?  Remember the analogy of a map being a book that you can read.  Highlight features, boundaries or landmarks.

Destination – A description of what your target is at the end of the leg.  This could be a trig pillar, the corner of a wood or a junction in a boundary etc.  It is also useful to highlight any other feature that would indicate an error in your navigation, this is known as a gross error check.

Staying On Course

It is all very well to have a bearing on your compass and start walking, but what if you drift to one side or the other?  This is not uncommon and can be caused by the slope of the ground or even a strong cross-wind.

drift

Exercise: Find somewhere safe such as a football field.  Stand on the long touch-line facing along the line (your bearing).  Now close your eyes and start walking.  After 25 paces stop walking and open your eyes!  The chances are you will have drifted off the touchline, we all do it.

We, therefore, need a way to stop this happening.  One has already been mentioned in Part Three, and that is picking a feature on the bearing and walking towards it.  But what if there are no features?

There are two very similar techniques which involves two people.  The first involves you setting off with your compass on the bearing, your colleague stays put and has a compass with the same bearing.  As you walk forward your colleague can advise you if you are drifting and tell you to move to the left or right.

land-navigation-part-3-31-728

The second has been used by me to good effect in very poor visibility (less that 10m).  The person with the compass remains still and sends the other person ahead to the edge of visibility or a reasonable distance.  That person stops when told and is then moved to the left or right until they are on the bearing.  At this point the compass holder moves forward to join them.  This process is repeated until you reach a recognisable feature or the end of the leg.

land-navigation-part-3-32-728

Exercise: Find somewhere safe such as a football field and go out with a friend.  Practice both procedures until you feel confident.

Transits & Back Bearings

When two objects are in the same line of sight, they are said to be in transit.  For example, if you are walking along a footpath and to your left your can see a fork in a river and behind it the corner of some woods in line with each other.  Then if you draw a line on your map joining these two points and extend it to the path that you are one.  This will give your position on the footpath.

transit 1
In the example shown, a transit is taken between two peaks either side of track.  When these are inline our position on the path is known.

However, you do not need two features in transit if you have a compass only one feature is all that you need.  Imagine you are walking a footpath with no unique features to allow you to identify your position (hedge boundaries etc), the sight of a single identifiable feature is all you require.

Take a bear on the feature and remove the GMA (rid for grid).  Now place this on the map with the long edge against the feature (direction of travel arrow pointing towards the feature), transfer the bearing onto the map and where it crosses the footpath is your position.  This is a back bearing

back bearing dart 1
In the example shown – rather that taking a bearing, when you are inline with the dam you will know exactly where you are on the ‘Two Moors Way’

Exercise: Plan a route near to where you live.  Work out some possible transits and back bearings.  Then go out and practice them until you are happy.


In Map Reading & Navigation – Part 5, we will be introducing you to Advanced Navigation skills – aiming-off, attack bearings and contouring.

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