Navigation 2017-04-08T21:25:15+00:00
Navigation

Finding Your Way

Your most valuable navigational tool is your own location awareness. A memory for detail, both from a map and observing your surroundings, should be developed. Make a point of learning to reconcile where you are on the map with your local environment.

Maps

Your map contains nearly all the information you need to use it: study it carefully, especially the margins. You should use a 1:50,000 scale topographic map, or a Parkmap, for which 1 centimetre represents 500 metres. In particular note that the height contours are 20 metres apart on these maps. Topographical maps are shaded as if the sun were to the north-west, making them almost impossible to interpret if upside down.

Look carefully and all the instructions to use a map are provided. Don’t forget to read all the fine print!

Standard six-digit grid references are given in the form “Map Number” XXXYYY where XXX is the easting and YYY is the northing, e.g. CA10 358487. The northings are read off the top, or bottom of the map and the eastings are read from the sides. Accuracy in this format is ± 50 metres. The full grid reference, as used by GPSs are in the form xxXXXxxE  yyYYYyyN, where XXX and YYY are the same as for the standard grid reference above, e.g. 1235800E 5048700N. The seventh digit gives your position to ± ½ metre. The first two digits in each case can be found at the bottom left hand corner of the map. When providing a grid reference to emergency services, always state which map format you are using ‑ NZMS260, or Topo50 ‑ and/or the map number.

If the grid references you have been given are in older NZMS260 map format, convert them to the current Topo50 map grid at www.linz.govt.nz, keyword: on-line conversions.

Compass

In New Zealand, Magnetic North is approximately 21° east of Grid North, the magnetic variation. Grid North is indicated by the vertical blue easting (or meridian) lines on the map and Magnetic North by the red needle on your compass. Skill limits and the quality of your compass allows you to achieve around ± 5° accuracy.

The easiest way to navigate is with a Silva compass, or equivalent with a line scratched from the compass centre to 21°. In the real world, always align the red (Magnetic North) needle to the 21° scratch to take a bearing. On the map, keep the compass north pointing to Grid North (i.e. the rotatable orientating lines parallel to the eastings) when taking a bearing. This technique does not require any magnetic variation calculations to be undertaken and is therefore foolproof.

Note that the magnetic variation drawing on the map is accurate, allowing you to orientate the map by placing the compass on the drawing and rotating the map and compass until the compass needle aligns with the Magnetic North line.

Using a compass

Ensure that the compass is always held close to the body and pointing straight ahead of you. Rotate all of your body, not just your shoulders, by holding the compass firmly to your waist with both hands when taking a bearing, looking straight up and down from the target to the compass. Ensure that metallic items (e.g. belt buckles, rifles and ice-axes) are not interfering with the operation of the compass.

When there is restricted visibility, set the compass to the correct grid bearing, hold the compass so it points straight ahead of you and rotate yourself until the compass needle north aligns to the 21° scratch. Locate an easily identifiable target as far away as possible along the bearing and walk towards it. When you arrive at the target, repeat the procedure. To retreat to where you came from, align the needle south to the 21° scratch.

To maintain a compass bearing in a whiteout, or difficult bush, the compass bearer navigates from the rear, calling out to the leader to veer to one direction, or the other.

When following a compass bearing to a distant, unseen target, deliberately aim off to one side of the target to reach a “handrail” – a river, or track that can then guide you to the target, rather than head directly to the target itself which could easily be missed.

Where there are identifiable features, take bearings on three features to triangulate your position. If you are beside a river or on a ridge, one or two features will suffice as you already know the baseline you are on.

Whenever you get to a reasonably long stretch of river, line up the compass with the river valley to get a feel for which direction the river is flowing and see where this coincides with the river shown on your map to give you a rough indication of your position.

On the tops, especially in foggy conditions, it is prudent to take compass bearings whenever ridges converge, to confirm that you are taking the right ridge, or spur.

GPS

Ensure that your GPS is set to the correct position format for the map you are using:

Correct GPS settings

GPS settingTopo50 mapsNZMS260 maps
Position formatNew Zealand Transverse Mercator 2000, NZTM2000 (based on NZGD2000)New Zealand Map Grid, NZMG (based on NZGD1949)
GPS Position format settingNew Zealand TM, NZTMNew Zealand, NZ
Map datumWorld Geodetic System 1984NZ Geodetic 1949
GPS Map datum settingWGS 84Geod Datum '49

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