A Guide to Map Reading
by Tony Harding

The Ordnance Survey (OS) is the national mapping agency for Great Britain , which produce a wide variety of map types and scales. The most suitable maps for walkers are the Explorer (orange covers) and Outdoor Leisure (Yellow covers), which between them cover the whole of Great Britain at a scale of 1:25000.

The Outdoor Leisure maps cover Britain 's most popular holiday destinations like the National Parks and Areas of Outstanding Natural Beauty in England and Wales , Forest Parks and National Scenic Areas in Scotland . There are 40 such maps available, all other areas are covered by the Explorer series.

There are 300 Explorer maps, which have replaced the old Pathfinder (green covers) maps. These maps have also been updated with more tourist information and places of interest. It is these series of maps that this guide has been based on.

Scale

The map, like a landscape photograph, is a gretaly reduced version of the land it portrays. A measure of this reduction is the 'scale' of the map. It gives a precise indication of the relationship between any measurement made on the map and its equivalent distance on the ground.

A scale of 1:25000, as used with the Explorer & Outdoor Leisure maps, means that 1 unit on the map represents 25,000 units on the ground. These units can be any length e.g.;

• 1 cm represents 25,000 cms or 250 metres.

• 2 mm represents 50,000 mms or 50 metres.

• 1 inch represents 25,000 inches or 694 yards.

• 2¼ inches represents 62,500 inches or approx 1 mile.

The distance between the north-south and east-west grid lines on the map is at 4 centimetre intervals which represent a distance on the ground of 1 kilometre.  

Map Reading

Reading a map, is the ability to interpret the various signs, symbols and other graphically produced information on a sheet of paper (the map) and relate to the countryside around you. The map does not have words to tell you if there is a steep hill, footpath, stream or forest, only the names of towns, villages, farms etc. Colours, symbols and abbreviations are used on the map to portray this information to the reader.

Once the main symbols are learnt and with a little practice, it should be possible to relate the countryside to these features and even form a mental picture of the land from the map without actually being there. It is necessary therefore to understand the common map symbols used.

Common Map Symbols
From OS Explorer/Outdoor Leisure Series

Vegetation
	Deciduous trees - randomly spaced
	Coniferous trees - randomly spaced
	Orchard trees - uniformly spaced
Contours & Heights
	Contour lines are at 5metre intervals in lowland areas and 10metre intervals in mountainous areas. The closer the lines are together, the steeper the gradient.
	Contour height numbers always point upwards and may be orientated in different directions. The hill shown has evenly spaced contours so the gradient or steepness is the same all round.
		Typical hill type formations.
Public Rights of Way (Not applicable to Scotland )
	Public Footpath - for use by walkers only
	Bridleway - for use by walkers, cyclists and horse riders
	Byway - for use by all traffic, including motor vehicles.
Roads and Paths (Not necessarily rights of way)
	Path
	Unfenced track or road
	Motorway
	Main, secondary, minor & unclassified roads.
	Gradient: Steep & very steep - note arrows point downhill
Railways
	Standard gauge: Multiple & single tracks
	Narrow gauge
	Road over, road under & station.
	Embankment - note direction of arrows point downhill.
	Cutting - note direction of arrows point downhill.
Boundaries
	County Boundary i.e. Beds & Bucks (not visible on the ground)
	Civil Parish i.e. Stanbridge & Tilsworth Parishes (not visible on the ground)
	National Trust areas - always open (NT oak leaf logo on purple background on new maps) National Trust areas - limited access (NT oak leaf logo on white background on new maps)
	National Park Boundary. (not visible on the ground)
	Lake , reservoir or pond
	Military firing and test range
	Field boundaries, i.e. hedgerow, wire fence or stone walls
General Features
	Church with a tower
	Church with a spire
	Church without tower or spire
	Greenhouse (nursery or garden centre)
	Electricity transmission line (pylon & pole positions are true locations)
	Triangulation pillar
	Viewpoint
	River with footbridge crossing and small stream
	Parking
	Picnic site
	Public House
	Golf course
	Public convenience, in rural area
	Telephone: Public/AA, RAC
	Camp site/ Caravan site
	Walks/Trail
Abbreviations
BP / BS	Boundary Post - Boundary Stone
CH	Club House
FB	Footbridge
MP / MS	Mile Post - Mile Stone
Mon	Monument
PO	Post Office in rural area
Pol Sta	Police Station in rural area
PH	Public House
Sch	School
W; Spr	Well; Spring
Note. A detailed legend of all signs & symbols used on Ordnance Survey maps is included on each Explorer & Outdoor Leisure map. This also includes the magnetic variation applicable to the area covered by the map and a guide to obtaining 6 figure grid references.

Grid Referencing

The national grid reference system of Great Britain involves breaking down the area around the British Isles into twenty-five 500Km squares. The squares are lettered in alphabetical order from A (top left) to Z (bottom right). The letter I is not used.

The six main squares, which affect our map grid referencing, are: H-J-N-O-S-T. These are represented below in the 6 bold squares. For example, Scotland and north England appear in square N and the east & south east of England appear in square T.

Each of the 500Km squares are further sub divided into another twenty-five 100Km squares, as shown with dotted lines below. 

Fig 1 -  The 500 Km Squares

This illustration again shows the 6 main 500Km squares in bold lines (H-J-N-O-S-T), broken down again into another twenty five 100Km squares. A second letter has been added to each of these 100Km squares based on the same 25-letter system as the main squares.

This clearly shows the two unique letters allocated to each of the 100Km squares covering the whole of Great Britain . For example, The Isle of Wight appears in square SZ and Leighton Buzzard appears in square SP.

Placing the unique 2 letters of the 100Km square in front of a six-figure grid reference prevents any confusion, as to its precise location within Great Britain . It should be noted that any 6-figure grid reference number would also exist in every 100Km square.

Fig 2 - The 100 Km Squares

The 6 Figure Grid Reference

An essential skill in map reading is the ability to identify any position on the ground with reference to its location on the map. The six figure grid reference is the accepted method of achieving this, which is accurate to within 100 metres anywhere in Great Britain .

It is always useful and sometimes vitally important for the map user to be able to describe precisely the position of a point on the map, for example:  

• To arrange a meeting place for a walk.

• To report a footpath problem to the local authority.

• To follow a guide book which uses grid references.

• To inform the emergency services of an injured persons location.

• To identify your location if using a Global Positioning System (GPS) receiver.

The OS map, with its National Grid reference system, enables us to locate any point in Great Britain with absolute accuracy.

Each 100Km square, shown at Fig 2, is broken down into one kilometre squares on the map. These are shown as thin blue lines, parallel to each other, in a north-south and east-west direction on the map.  These divide the map into squares and form the frame work of the grid reference system Each line is identified by a two-figure number. The lines are spaced at the map equivalent of one kilometre on the ground  i.e. 4 centimetres on the Explorer maps.

The grid lines are numbered around the edges of the map from 00 to 99, increasing in number from west to east and from south to north. Every tenth gridline is slightly thicker. Around the edge of the map, the area between each grid line is divided into tenths to assistance with estimating the grid reference.

All grid references are based on the southwest (or bottom left) corner of the appropriate 1Km square in which the feature appears. The horizontal numbers along the bottom (or top) of the map are always taken first. The vertical numbers along the sides of the map are then taken and added afterwards.

Note: it is very important to remember this and not get them the other way round. One easy way to remember it is to compare the map to a squirrel.

The squirrel runs along the ground (bottom of the map) before climbing up the tree (side of the map).

Fig 3 is a representation of a typical section of a map, showing some common symbols which will be used as an example to explain how a Grid Reference (GR) is obtained.

Example No 1; to find the 6 figure GR of the footbridge (FB), proceed as follows:

• Identify the 1Km square in which the FB appears, this is easy as the map only shows one full square. This is 36 - 11, remember it is always with reference to the southwest or bottom left corner of the square. Also remember the squirrel !! Hence 36 first and not 11.

• Draw an imaginary line from the FB to the bottom of the map and count the tenths to the right of the No 36 grid line, i.e. 7.  

• The first half of the GR is therefore 367.  

• Draw an imaginary line from the FB to the side of the map and count the tenths above the No 11 grid line, i.e. 8.

• The second half of the GR is therefore 118.

• The 6 figure GR of the footbridge is 367118.

All grid references should include a description of the feature, i.e. The footbridge at GR 367118. As the same 6 figure GR will be repeated in every 100Km square over the length and breadth of Great Britain , the unique two letter prefix should also be added (see page 9) to prevent any confusion. For example if the map was from the Isle of Wight , the true GR would be the footbridge at SZ 367118. However for most purposes this is of little consequence, for even the most inexperienced map reader is unlikely to find themselves 100Km (60 miles) from where they think they are!!

Fig 3 - Typical Map Section

Example No 2; to find the 6 figure GR of the hill top, proceed as follows:

• Draw an imaginary line from the hill top to the top (or bottom) of the map and count the tenths to the right of the No 36 grid line, i.e. 1.

• The first half of the GR is therefore 361.

• Draw an imaginary line from the hill top to the side of the map and count the tenths above the No 11 grid line, i.e. 8.

• The second half of the GR is therefore 118.

• The 6 figure GR of the hill top is 361118.

Example No 3; to find the 6 figure GR of the church, proceed as follows:

• Draw an imaginary line from the church to the bottom of the map and count the tenths to the right of the No 37 grid line. This is actually on the grid line so it is at 0 tenths.

• The first half of the GR is therefore 370.

• Draw an imaginary line from the church to the side of the map and count the tenths above the No 11 grid line, i.e. 3.

• The second half of the GR is therefore 113.

• The 6 figure GR of the church is 370113.

Q1  Suppose you had agreed to meet a friend at the car park at GR 365115, which car park would you go to?

Q2  What is the grid reference of the electricity pylon next to the river?  

Q3  Your friend falls and breaks a leg at the junction of the footpath and bridleway. You call the ambulance service on your mobile phone for help, but what grid reference do you tell them?

Q4  What feature is located at grid reference 362109?

Setting the Map

When out in the countryside and unsure of your position, being able to relate landmarks and features around you to the map is essential if you are to identify your position. To identify your position, the map must be set or orientated. This means that the top of the map is facing north, use a compass if you are not sure where north is.

Look around and pick out two or more recognisable landmarks, i.e. a church, a hill top or woodland. Find the sign or symbol of the landmark on the map. Rotate yourself and map together, until the chosen landmarks are in line with their position on the map. Other features should now fall into place, the map is now correctly Set.