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How to read an IGN (Ordnance Survey) map and find your way?

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The ability to read a map properly is extremely useful in providing you with all you need to know about what to expect on the hike.

 

Why learn to read a map

A map shows the terrain on a horizontal plane as seen from above, in the form of a simplified diagram. Some training is therefore required in order to see the connection between the map and the terrain. Very soon, you'll be hooked. To prepare your hike or find your way, your map will always be there to help, and unlike GPS and telephones, it never runs out of battery. Remember to also take a compass to never lose your bearings.

 

Choosing the right scale

For a hike, the ideal scale is 1:25,000, i.e. a map in which 1 cm is equivalent to 250 m or 4 cm is equivalent to 1 km. It can be used to view each detail (watercourse, forests, paths, etc.) and to accurately work out where you are. This scale is found in the Blue and TOP25 Series IGN maps. For those hiking under the rain, there are TOP25R maps ("R" for "Resistant"), waterproof, tear-proof and printed on both sides to save space in your bag.

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carte-code-couleurUnderstanding colour codes

The colours used on the map are important as they identify the type of terrain.

  • Green represents wooded areas
  • White represent meadows and fields.
  • Blue for bodies of water (lakes, rivers, etc)
  • Orange usually for contour lines
  • Black is very common and refers to all human constructions; it also identifies rocks and scree.

Good to know: You will see areas that are more or less dark. The shaded areas that cover the slopes or mountain sides give a sense of the relief. By convention, the theoretical shading shown represents the effect of the sun shining from the north-west at an average angle of 45°. Rather than being useful for identifying where you are, it is simply a tool that makes it easier to identify the slopes when reading the map.

 

Use the four layers of information to get your bearings

To be as precise as possible, the map layers four types of information of natural or human origin.

 

  • The relief:

The contours provide additional information about the differences in elevation by defining the volumes and general shapes formed by the terrain. A contour line is an imaginary line that links all the points of equal elevation. On 1/25 000 maps, the contour lines are every 10 metres. . For example, you will climb 50 m of vertical rise every five lines. The closer the contour lines, the steeper the slope. Conversely, spaced-out contour lines mean that the relief is less hilly and gradients gradual. Remember your poles to help you climb and increase your safety when going downhill.

  • Bodies of water:

Rivers, lakes, wetland, the sea, etc are always represented. Waterways have always been very useful to lost hikers. Most villages were traditionally built on the banks of a river, and walking upstream or downstream would take them back to civilisation.

  • Human developments:

Buildings, roads, paths as well as communications and power lines are shown in black.

  • Toponymy:

This term means the study of place names. Depending on the precision of your map, you will be able to read the names of the smallest villages and the largest cities. Summits and forests are also named.

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Finding notable features

Details that can often be used to work out exactly where you are. The map maker ensures that all notable natural or human-made features in a location (a spring, a chapel, a cross, a bridge, a ruin, an isolated tree, etc) figure on the map. By referring to the key on the map, you will easily identify the features.

 

POSITIONING YOUR MAP WITHOUT INSTRUMENTS

By convention, north is located at the top of the map. You can rotate the map held horizontally in front of you so as to align the features of the terrain with the map's symbols and point your map in the right direction.

 

 

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