CAVRA Service Materials

4. Conservation and Access

• Out in the Country, published by The Countryside Agency.

5. Navigation with Map and Compass

MAPS :

• different scales:
  for us: either 1 : 25,000 or the more detailed 1 : 50,000
  (-- but a square is always 1 km by 1 km !)
• six-digit grid-references:
  east-ing and north-ing (like x, y -coordinates, at 100 m accuracy): the national grid;
  the Ordinance Survey: our 'patch' of the coast is on Sheet 170 of the OS 1 : 50,000 series;
  note that the six-digit grid-reference is the same every 100 km N and S, E and W (-- why?)
• reading contour lines:
  
  maps (at least most maps now) have contour lines every 10 m, with a thicker line every 50 m of height difference;
  recognising features on the map, such as a hill-top, valley or re-entrant (cwm in Welsh,) ridge or spur, saddle point (or pass, or col, bwlch in Welsh,) etc.;
• meanings of symbols used on our maps:
  
  paths, powerlines, public rights of way, triangulation ('trig') points.

ROUTE PLANNING :

• having some familiarity with 'our' area, in the National Park:
  from W to E: Black Mountain, Brecon Beacons, Black Mountains;
• deciding on 'sensible' routes, e.g.
  following contour-lines (to avoid losing height,)
  avoiding walking diagonally up or down a slope,
  walking to and walking along obvious features of the landscape,
  choosing a suitable place for over-night camping;
  
• Naismith's rule, to estimate the time required for walking:
  12 mins for 1 km of horizontal distance covered, plus
  10 mins for each 100 m of vertical height climbed or descended;
  note (i) that often we cannot just take the difference in altitude between the beginning and end of a section, and (ii) that descending a steep slope can be as slow as going up it;
• bearings, use of a compass:
  the bearing of a direction is the angle it makes with the N, measured towards the E (i.e. clockwise): so N is 0º, W is 270º, SE is 135º;
  note: magnetic N is 4º to the W of true N (in our area, now,) hence we have to add 4º when going from map to reality;
  from the map:
  1. place the edge of the compass in the direction of the walk,
  2. turn the dial on the compass so that the red arrow points N (up) on the map,
  3. turn the dial 4º (= 2 divisions) further, and read off the angle: this is the magnetic bearing (see below;)
• writing out a detailed route card:
  for use by the group, but must be understandable by anyone;
  start a new leg (= section) when there is a change in direction which does not follow a landmark;
  include the initial (!) magnetic (!) bearing for each leg, and a useful description: you cannot see contour lines in the field;
  Example:
  [The colours and position of this table come out the way they should in Internet Explorer, but still not in Netscape Navigator v 4.7 -- and I actually removed again the work-arounds I had put in, because they added too much clutter. Sorry.]

  Grid Ref.	Initial Bearing	Distance	Time (use Naismith)	Cumulative Time	Additional Notes
  033585	44º	1.5 km	30 min	30 min	walk down to bwlch
  043596	62º	2.6 km	71 min	1 h 41 min	up the ridge to trig point
  066608	...	...	...	...	...

• 'aiming off',
  to find a point (like a car park) along an extended feature (like a road):
  problem: aiming directly for the point (car park,) one might miss it on one side or the other, and not know whether to turn left or right when one has reached the feature (road;)
  solution: deliberately aim to the left (or the right) of the point, and then turn right (or left) when you have reached the feature;
• planning escape routes.
  it is part of planning a route to write down, for each part, an easy to find alternative, in case of a medical problem, say, or sudden bad weather,
  e.g. ''escape route: keep heading W to the road.''

IN THE FIELD :

• to walk on a bearing:
  1. turn the dial on the compass to the magnetic bearing (see above,)
  2. turn the whole compass until the red arrow is lined up with the red N needle,
  3. walk in the direction of the compass;
• to walk on a bearing more accurately;
  use 'attack points' (on difficult ground): find a landmark, like an obvious tree, which is on the right bearing, and walk towards that (taking any route;)
  'leap-frogging' (in mist or snow, on a slope, when it is very windy, etc.): one person walks ahead, their direction checked by those behind, (who are not moving and) who then follow;
• to estimate the distance walked,
  use 'pacing': 60 double-steps are approximately 100 m,
  (-- this depends on the person, of course, and you need to know how many double-steps you take in 100 m;)
• to check one's position:
  using the slopes of the ground and other features within one's sight;
  resection:
  1. point the compass towards a distinct feature, and turn the dial so that the red arrow is in line with the red N needle;
  2. subtract 4º, i.e. turn the dial back by 2 divisions, (and then don't turn the dial again;)
  3. place the compass on the map, and move the whole compass so that the red arrow points N (up) on the map;
  4. draw a line through the feature on the map, in the direction of the edge of the compass: you are somewhere on that line;
  5. repeat the process for another feature: you are then near the intersection of the two lines
     (-- the result is more accurate if the two features are at an angle of about 90º from your position.)