Maps and Compass Navigation

Grid References

• The country is divided up into 100 km squares, each with a specific two letter sequence, e.g. NX. You can find this in one of the corners of an OS Map.
• OS Maps have a 1 km grid on them, you can use this to get 1 km of accuracy e.g. NX6543. (65 KM from west to east into the square, and 43 KM from north to south into the square).
• They are often subdivided up into 100 km sections.To be as accurate as possible, you can use a compass 1:25K scale. See below for an example where the exact 6 digit grid reference is SX659690.

- If you can want to convert between GPS coordinates and UK grid references, you can use this handy tool

Contour Lines

• The yellow lines on an OS map.
• They can be used to identify the steepness of the terrain.
• The legend/key will specify the interval of the lines. On most maps this will be 10 m. Sometimes it may be 5 m.
• Remember that if the contour line resolution is 10 m, then a feature 9 m tall will not appear on the map.
• It is sometimes helpful to think of contour lines as if they were high tide marks on a beach.

Compass 3-Step Navigation Method

1. Point the compass on the map between where you are now and where you want to go. Then, align the compass north with the map north.
2. Add the magnetic variation to your bearing by rotating the compass housing. This adjustment can be found on the map legend.
3. Align the magnetic north arrow with the north on the dial. Then, walk in the direction indicated by the direction arrow.

Orientating Yourself

Transit Lines

A transit line is a clearly identifiable line in the land that intersects with your route. If you are unable to get two objects to create a transit line, you may wish to use two objects with two separate transit lines to be more accurate. When you can see the transit line, you know where you are.

Here, the transit lines are the light dashed lines.

Pinpointing with a Compass (Back Bearings)

You can use a distinct feature that you can see around you that is also on the map to identify your position along a track.

1. Use your compass to get a bearing for the point on the landscape that you have noticed.
2. Adjust your reading for magnetic variation.

3. You can track you compass (oriented north) along your route until the direction of travel arrow lines up with the point you measured the bearing of. When it lines up, this will indicate your current position.

   Triangulation Rresection)

If you are not a known track, you can use 3 back bearings to triangulate your position. Ideally, they should be 120° apart.

Aspect of Slope

If you are completely lost, but know which 1 km grid square you are in, this technique can be handy.

1. Stand facing down the slope.
2. Take a compass bearing pointing down the slope, this is called the aspect of slope.
3. Use your compass to estimate which slope you are on in the grid square you think you are in.

Walking Speed - Naismith’s Rule

Naismith created a rough formula for estimating walking time. In rough terms he suggested that: - On flat ground it is ~5 km/hr - Accent, it takes about 30 minutes for every 300 m, or 1 minute per 10 m contour line - Decent varies in speed, sometimes you are much faster than on flat ground, sometimes much slower, however, this tends to averaged out.

Here is a handy calculator that you can use to estimate how long a route will take to walk.

Walking on a Bearing

Once you have got your bearing, you can use an object either in the far distance or an object that is closer (ideally 500-1000 m) away to walk towards.

Aiming off

If you are aiming for a linear feature such as a gate in a fence, aim your bearing to one side of the fence. Once you have reached the fence, you will know which direction to correct in and will not have to guess in poor visibility.

Attack points

If you are aiming for a less distinct feature, it may be useful to aim for a more prominent feature to get close enough. This prominent feature is called an attack point. Once you have reach the attack point, you can take a new bearing and navigate to the less distinct feature.

Search Patterns

If you are unable to find the feature you are looking for, you may wish to use a search pattern to help you find it.

Spiral Search

This method is ideal for when you are alone and have limited visibility.

1. Walk north to the limit of your visibility
2. Turn 90° and walk twice the limit of your visibility
3. Turn 90° and walk three times the limit of your visibility
4. Repeat this until you find what you are looking for.

Sweep search

If you have a party of walker, everyone can be spaced out to the limit of visibility and walk in a single direction. The line can then sweep over the search area.

Further Reading

These are the key materials that I used in making this document.

• ORDNANCE SURVEY MAP READING From the beginner to the advanced map reader (available as a PDF)

Digital Tools I Use

Maps

Bing Maps

This is only useful in that on a desktop browser you can get 1:50K and 1:25K OS maps.

OSMAnd

Mobile app that allows you to use both open street map mapping as well as many map APIs, including Bing Maps.

OS Maps App

Not very well engineered, and often unreliable. However, get the mobile app (don’t bother with the subscription) and redeem your paper map codes. I tend to just use it as a standard paper map but with my “known” location as an added bonus.

OS Locate

Mobile app that gives your UK Grid Reference. You can have it give you your 6,8 or 10 digit reference. It has a compass feature, but I would not rely on it.

Google Earth

The best way I have found to view satelight imaging. Allows you to get a good lay of the land and offers a different perspective to a topo map.

Metoffice app/website

The best weather forecasts for the UK.

GPS to UK Grid

Sometimes you may need to convert between GPS Coordinates and UK Grid references, this is a handy tool I built to do that.

Walking time calculator

A handy tool calculate your walking distance that I built.

Emergency Trip Plan Info

A tool that I built to help build out something a bit like a route card that you can share with someone you trust to help make sure they have all the information they need when you go outdoors.

Magnetic Declination

Get the current magnetic declination information.