Navigation and map scale

We are incredibly fortunate in the UK to benefit from such a detailed mapping system as that provided by the Ordnance Survey maps. Further a field even today there are areas with so little detail mapped that the best scale map you might acquire for the area may be 1:1,000,000.

Scale is one of the first things to appreciate on your map and is expressed as a ratio. One of the most commonly used map scales in the UK by outdoor enthusiasts is the 1:25,000 OS Explorer. The 1:25,000 gives you a very high level of ground detail whilst still covering a large enough area of ground to contain significant route distances. Occasionally your route will require you to carry two or if its a circular route maybe even three or four 1:25,000 maps.


The higher the second number in the ratio gets the larger the area of ground the map covers but the amount of actual detail realting to that ground is reduced on the map (the above road touring map ratio of 1:1,000,000 for example) as it would appear too squashed up and complicated to read accurately. Conversely the smaller the second number in that ratio becomes the more restricted the map area coverage becomes but the detail of that area of ground increases; a 1:10, 000 orienteering map for example.

One of your first tasks as navigator is to decide which map scale will suit your intended activity best?


Cycling UK – French Alps, covering circa 70 miles per day.


Descending from Ben Nevis plateau in poor visibility.


Recceing the race route for Yorkshire Three Peaks.


Teaching orienteering skills.

Each of the above examples could arguably have a different scale of map to best suit the demands of that activity.

The vast majority of mountain walkers opt for 1:25,000 maps for the incredible detail they show and the sheer volume of reference points you gain at that scale. However if you are walking for very long distances a 1:50,000 scale cuts out half the detail but covers twice the area meaning you wont need to carry as many maps and still provides you with a wealth of ground shape detail.

If your walk is relatively un-complex and mainly on established routes and tracks the 1:50,000 will be more than adequate and once you begin to interpret contours readily into actual ground shapes the 1:50,000 scale can actually be ‘easier’ on the eye to determine ground shape as it less clustered with detail.

If however your intention is to get yourself off route into really wild terrain with no tracks and way marks to guide you then the 1:25,000 jumps to the fore as a real bonus tool even detailing prominent rocks in the landscape on occasion! Of course as your level of navigation improves you will learn to use both map scales interchangeably to stay found in the outdoors.

Ultimately scale is a way of expressing how distance on the ground in your environment relates to measurable distance on your map in front of you. The sooner you can become conversant in how mm’s and cm’s measured on your map translate to m’s and km’s to be covered on the ground the sooner you will be able to overview a map at a glance and develop a minds eye appreciation of what to expect along your route.

On the 1:25,000 OS explorer map for example, you will see the entire sheet is overlaid with a faint blue grid (more on this in future blogs) with each individual square measuring exactly 4 cm’s on the map and representing a 1km square of terrain. Any 4cm measurement anywhere on your 1:25,000 equals 1km on the ground and so immediately you can begin appreciating route distance simply by seeing how many of these map squares you pass through.


1:25,000 OS explorer map with 4cm grid squares.

Taking this further then if 4cm = 1km, 2cm = 500m, 1cm = 250m and finally the smallest measurement you are likely to take from any map is 1mm and is equal to 25m on the ground in this example.

Spend some time familiarising yourself with the above scale measurements of the 1:25,000 and remember that the ability to accurately measure distance on the map and translate this into distance to be covered on the ground will be crucial to your skills of both pacing and timing which we will cover in later blogs.



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