Basic map and compass skills are often overlooked by paddlers but are essential if your not just paddling the easy to get to waterways or are trying to scout a hidden stout for a first descent.
Global Positioning Satellite (GPS) technology has changed many aspects of navigation. This doesn’t negate the need for a basic understanding of map/compass use. Batteries don’t last forever and you just know that if your in a tight spot your GPS is bound to breakdown! However that said if you need to pin point your position in bad weather (or otherwise) a GPS will do it damn quick.
This page provides a basic introduction to navigation techniques, the kind of kit you should be carrying, and references to other sites and resources that can be used to help further develop your knowledge base.
Navigation kit to carry
Map of area being paddled (I prefer OS 1:25K weatherproof maps).
Compass (nothing fancy, basic will do e.g. Silva 7NL)
Spare GPS batteries
Waterproof OHP marker pen to mark maps (if its a plastic covered one)
Scale: is the degree of reduction used for the map. For instance 1:25000 would indicate that 1 cm on the map corresponds with 25000 cm (or 250m) in real life.
1:50000, 1cm on the map = 50000cm in real life (500m), so 2cm = 1km
1:25000, 1cm on the map = 25000cm in real life (250m), so 4cm = 1km
Longitudinal Lines: are the imaginary vertical lines that run across the globe from north to south.
Latitudinal Lines: are the imaginary horizontal lines that run across the globe from east to west.
Magnetic Deviation: good topographic maps will give you the so-called magnetic deviation which is the difference between Grid North (on the map) and magnetic north (on the compass) for the specific locations on the map. Using this information you can adjust your compass readings and assure yourself of the absolute northern direction. When taking a bearing from a map using a compass you would add the deviation to get the magnetic bearing. (In the UK this is around 3 degrees, but this does change as Magnetic North is not a fixed point!).
Taking a bearing: line the edge of your compass so that is joins Point A (your position) to Point B (your intended destination). Turn the bezel of the compass so that the North Arrow points to north on the map (to the top). Turn the bezel 3 more degrees to add the magnetic deviation for the UK. Take the compass off the map and whilst holding level turn the compass until the north pointer (usually red) lines up with north on the compass bezel. The direction of travel pointer on the compass base indicates your direction of travel.
100km square identifier: Every 100km x 100km square in Britain has a unique two letter identifier which forms the first part of a grid reference. OS maps can cover parts of two or more of these squares.
Grid Reference: A grid reference is used to identify a single point on a map. There are generally two parts to a grid reference. The 1st is two letters that identify the 100km square being used and the 2nd part is the six figure grid reference is made up of two groups of three numbers.The first group describes the easting. Easting’s are the vertical lines that increase in value from left to right. The first two numbers are the printed easting line to the left of the point to be identified. The third number is the number of tenths of a printed square to the right of the printed easting line that the point is situated.
The second group describes the northing. Northing’s are the horizontal lines that increase in value from the bottom to the top. The first two numbers are the printed northing line directly below the point to be identified. The third number is the number of tenths of a printed square to the above that printed northing line that the point is situated.
Grid references with more than 6 digits just offer greater accuracy.
Image produced from the Ordnance Survey Get-a-map service.
Image reproduced with kind permission of Ordnance Survey and Ordnance Survey of Northern Ireland.
The centre of the Tarn (that is highlighted by the red circle) has the grid reference NY233 149.
The Church (that is highlighted by the green circle) has a grid reference of NY258 139.
The road junction (that is highlighted by the dark blue circle) has a grid reference of NY231 136.
The small building (that is highlighted by the pink circle) has a grid reference of NY256 152.
Legend: The legend explains the meaning of symbols and the meaning of the line colors/styles used on the map.
Trails, roads, train tracks, cable car lines, boat routes: maps use different colors, line style or symbols to indicate the public rights of way, tracks and roads on a map.
Other Natural and man-made features: besides trails and roads most maps will have symbols for major features like bridges, houses, crags/cliffs, waterfalls, rivers, lakes, etc. Using these features will help you to determine your location on the map.