Ultimate Navigation Part 10: the question of scale

As summer approaches, a map can often be the only navigational tool you bother using – but which mapping scale is best? In PART 10 of our navigation series, Lyle Brotherton explains how to interpret them.

"Thanks to the creation of the Ordnance Survey on 21st June 1791, in Great Britain we are fortunate to have the best maps in the world. Originally all Ordnance Survey mapping used Imperial measurements: miles, yards, feet and inches. Today they all use the much simpler metric system (kilometres, metres and centimetres) and we also have access to other excellent maps available from Harvey Maps."


The tricky part: map scales!

The scale of a map shows how much you would have to enlarge your map to get the actual size of the piece of land you are looking at. It is expressed as a ratio and is always printed on the map.

If your map has a scale of 1:25,000, this means that every 1 unit on the map represents 25,000 of those same units of measurement on the ground. These maps use metric measurements and we navigate using metres and kilometres, so using the aforementioned ratio 1cm on the map equals 25,000cm, or 250m, on the land. This means that every 4cm on a 1:25,000 map = 1km in real life. To make life easy the blue grid lines (grey on Harvey Maps) are exactly 4cm apart, so every square is 1km by 1km.

The first number (map distance) is always 1. The second number (ground distance) is different for each scale – the larger the second number is, the smaller the scale of the map. This sounds confusing, but in fact it is easy to understand. Large scale maps show small features on the land, such as an individual house. Small scale maps show large features, such as an entire city. So, a 1:50,000 map has large area (and therefore less detail) on one sheet, whereas a 1:12,500 map has a small area (and therefore more detail) on the same space.

The most popular maps

1:50,000 scale

Ordnance Survey Landranger Maps
204 of these pink-sleeved maps cover the whole of Great Britain. You’ll find footpaths, rights of way and some tourist information features on these maps, but you do lose some detail as compared to smaller scale maps such as the 1:25 000. This means you won’t find minor paths, field boundaries, open access areas and public rights of way, or smaller areas of marshland, rocky ground or small streams on these maps. However, don’t be put off Landrangers, because they do have their place in walking and mountaineering. Indeed, some Scottish Mountain Rescue teams use these as standard issues where fences and rights of way are unimportant and where they need to view larger areas of land.

Why should I use these?
In places where the terrain is extremely complex or very spread out, too much detail can become confusing and the 1:50,000 scale is easier to follow.


1:40,000 scale

Harvey British Mountain Maps
Centred around specific mountain locations in Britain, these have a large area of clear, detailed mapping on one sheet. Layer colouring is used for easy ID of hills and valleys. With detailed enlargements of selected summits, climbers’ crags are highlighted too. Mountain incident info is included, as well as a BGS (British Geological Survey) map of the geology of the area.

Harvey National Trail Maps
All the detail needed for sure navigation of your chosen National Trail is shown, with 100 miles of detailed mapping on one sheet along with an introduction to the route. Directions to the start, facilities available in towns and villages, information on finding accommodation, camping and food, plus ranger service contacts are all shown.

Harvey Ultramaps
Slim, light and pocket-perfect (weighing 25gms), the unique folding pattern of the compact Ultramaps allows you to open to either side of the sheet. They show all the detail you‘d expect on a large-scale walking map, including boundaries, walls, fences and rights of way.

Why should I use these?
Like the 1:50,000 scale, these 1:40,000 maps are often preferable in confusingly contoured landscape when a more general view of the shape of the land is required.


1:25,000 scale

Ordnance Survey Explorer Maps
403 of these orange-sleeved maps cover the whole of Great Britain (with the exception of the Isle of Man, which is excluded from this series). They show the detail of Britain’s landscape, minor paths, field boundaries (walls and fences), open access areas and public rights of way (except in Scotland where the ‘right to roam’ act covers most land), and small areas of marshland, rocky ground and small streams.

Harvey Superwalker Maps
Like the OS Explorers the 1:25,000 scale of the Superwalkers shows land shape in clear and accurate detail. However, although public footpaths, bridleways and other key features are shown, these Harvey maps do away with information irrelevant to the walker, making them appear less cluttered than their Ordnance Survey equivalents.

Why should I use these?
Because of the extra detail shown they are superb for micro-navigation when you need to be able to identify as much of the terrain as possible.


1:12,500 scale

Harvey Summit Maps
Although they only cover an area of 4x3km, the extra close-up version of Harvey’s maps are used by some Mountain Rescue teams as they are excellent for complex ridges such as the Cuillin on Skye.

Why should I use these?
For navigating super-complex mountain summits like those on the notoriously difficult Cuillin Ridge, these maps offer an extremely clear view.


 

BE AWARE!

Tourist features in blue ink (nature trails, visitor centres and – importantly – ski-lifts) are not placed accurately on any of the above maps. They should NOT be used as navigation aids.

 

Important considerations when choosing your map

Durability: Using a map cover will protect your map, but these can be unwieldy and you may need to take a paper map out to refold it as you move across terrain – not ideal in the rain. Laminated maps are waterproof and these are good, but my preference is maps that are printed directly onto a plastic material (look out for Harvey XT series, printed on lightweight polypropylene) as these fold more easily and are less cumbersome.

Buy the most up-to-date maps you can: From the minute they are produced maps start going out of date. New OS maps come with a free digital version of the sheet, which will update automatically – but, of course, your paper map will not!


CUSTOMISE YOUR MAP

I place a great deal of emphasis on manually personalising and updating maps; you should do so too. Annotate your maps, indicating streams that have dried up, paths that are incorrect, a rock fall or wash-out, unmarked potholes, new tracks, overgrowth, scree and great areas to wild camp.
— Lyle Brotherton