ORDNANCE SURVEY MAP READING

O R D N A N C E S U RV E YMAP R EADI N GFrom the beginner to theadvanced map reader

ContentsWhat is a map?3 Understanding your map needs4 Map symbols5 Map scale6 The basics8 Grid references10 National Grid lines11 Reading contours and relief13 Know your compass14 Using your compass15 Using land features17 Advanced techniques17 Pinpointing your location17 Transit lines18 Pinpointing your location with a compass19 Triangulation20 Aspect of slope21 Feature interpretation22 Contouring23 Measuring the distance travelled on the ground24 Naismith’s rule24 Walking on a bearing26 Still can’t find your next location?27 Navigating at night or in bad weather32

What is a map?A map is simply a drawing or picture of a landscape orlocation. Maps usually show the landscape as it would be seenfrom above, looking directly down. As well as showing thelandscape of an area, maps will often show other features suchas roads, rivers, buildings, trees and lakes. Crown copyrightA map can allow you to accurately plan a journey, giving a goodidea of landmarks and features you will pass along the route,as well as how far you will be travelling.Understanding your map needsThere are many different types of maps. The type of map youwould choose depends on why you need it. If you were tryingto find a certain street or building in your home town youwould need a map that showed you all the smaller streets,maybe even footpaths in and around town.If you were trekking across a mountain range you might need amap that shows a bigger area of land and tells you the heightsand steepness of the mountains.If you were a pilot flying from London to Edinburgh you mightneed a map that has the whole of the country on a single page,with only the locations of towns and cities on it. Whichevertype you choose, there are a few basic features usually foundon any map, which will be explained in this leaflet.3

Map symbolsRather than containing descriptions, maps have symbols toshow where certain things are. Symbols are used so mapsdon’t have to be covered in writing, as this would make themvery confusing. Ordnance Survey uses different shapes, coloursand symbols to show all the roads, buildings, rivers and otherfeatures of a landscape. Symbols are designed to be simple,often looking like the features they represent. This meansthings can be quickly and easily recognised as you look at amap. The symbols here are actually used on Ordnance Surveymaps. Write down what you think they represent:123Use the blank boxes to draw pictures of how you think thesymbols for the following things appear on a map:a. Horse ridingb. Gardenc. Place of worshipd. Lighthousee. Nature trailf. ViewpointHere’s where you find out how you did The answers to the first three questions are a telephone callbox, a campsite and a caravan site. To find out how close yourdrawings are to actual Ordnance Survey symbols you can lookat the key on an Ordnance Survey map. Maps will usually have akey or a legend. This is a section that will explain what each andevery symbol on the map represents. If you find something onthe map you don’t understand or recognise, the key or legendwill help you to identify what it is.4

Map scaleTo create an accurate picture of a landscape on papereverything has to be made much, much smaller. This is doneby ‘scaling down’ the actual size of the land. The map belowshows Great Britain. The size of the island has been ‘scaleddown’ so it will fit on this sheet of paper. The map is too smallto contain a lot of detail and doesn’t have many names on it, asthere isn’t much room.Scale: 1:6 000 rburghInvernessFort mpbeltownStranraerNewcastle upon TyneCarlisleIsle of ManKendalDouglasLeedsKingston upon ton

The basicsThere are some basic features that most maps will include: Roads tend to be marked in different colours depending onthe type of road depicted. Roads on a map range from thickblue lines, showing motorways, to dashed lines, indicatingan unfenced minor road. Footpaths are marked on Ordnance Survey maps in variouscolours. On a 1:25 000 scale OS Explorer map the publicrights of way are marked in green and on a 1:50 000 scaleOS Landranger map they are marked in magenta. There arevarious types of public rights of way and public access, soplease check the map key for full information. It is importantto be aware that footpaths that are shown in black are notnecessarily public rights of way. Woods are shown in green with a coniferous ornon‑coniferous tree shape printed over the top. Buildings are marked by small brown squares outlined inblack. However, some particular buildings have their ownspecial symbols, such as churches and windmills. Any ofthese buildings can be useful landmarks, helping you tocheck your position on the map. Rivers and streams are shown as blue lines. The width of theline is representative of the watercourse width (if the widthof a river is more than 8 metres it is shown as two blue lineswith a light blue area between). Rivers and streams can beextremely useful in determining your position on a map. Scale tells you how much the land has been scaled downto fit on the paper. If the scale of a map is 1:50 000 theneverything on the map will be 50,000 times smaller than it isin reality. Your Ordnance Survey map will also contain other featuresand information that will be explained, along with thefeatures above, in the key of the map.The following pages shows a scale comparison between1:25 000 scale and 1:50 000 scale6

Crown copyright1:25 000 scale1:50 000 scale7 Crown copyright

Grid referencesOrdnance Survey maps are covered in a series of faint blue linesthat make up a grid. The lines have numbers accompanyingthem that allow you to accurately pinpoint your location on amap. Once you have located where you are, the grid systemmakes it simple to give others (such as Mountain Rescue) anaccurate description of your location. This description, whichwill be a series of numbers, is known as a grid reference.Northings (up the stairs) »Before you begin to look at grid references it is important to beaware that all the numbers going across the face of the map,for example, left to right, are called eastings (this is becausethey are heading eastward), and similarly, all the numbersgoing up the face of the map from bottom to top are callednorthings (again because they are heading in a gs (along the corridor) »There are two main types of grid reference: 4-figure – for example, 1945, this identifies a single kilometresquare on an OS map. 6-figure – for example, 192454, identifies a 100 metre squarewithin a single kilometre square on an OS map.The Grid reference is always for the bottom left-hand corner ofthe grid square you are in.4-figure map referencesWhen giving a 4-figure grid reference you should always givethe eastings number first and the northings number second,very much like when giving the reading of a graph in school– you must go along the corridor (horizontal) and then up thestairs (vertical).8

Northings (up the stairs) »4746454412344342181716201921Eastings (along the corridor) »For example, the number 2 in the diagram is 19 across and45 up and therefore the 4-figure grid reference is 1945. Thenumbered squares on the diagram would have the following4-figure grid references:1 1845 2 1945 3 1844 4 19446-figure map referencesHaving worked out the basic 4-figure grid reference, forexample, square 3 above, imagine this square is further dividedup into tenths. Using the example right, the blue box is in thesquare 1844. More accurately it is 7 tenths across and 8 tenthsup within the grid square 1844 and therefore has the 6-figuremap reference 187448.The shapes on the diagram would have the following 6-figuregrid references: 185443Northings (up the stairs) » 18744845987654321441812435678919Eastings (along the corridor) »9

National Grid linesAs well as numbered grid lines, OS maps have a two letter prefix.The two letter prefixes can be found printed in faint blue capitalson OS maps. The whole of Great Britain is divided into squaresof 100km and each square is given two letters. There will be adiagram within your map’s key showing you which areas of yourmap fall into different squares of the National Grid.When you quote your grid reference you should put thetwo letter prefix of the area you are in before the numbers.This means that there is no doubt or confusion about yourlocation. For example, you may be at grid reference 509582 insouth‑west Scotland. The complete grid reference you shouldquote would be NX 509582 (without the letters the numericreference would be repeated in every 100km square).HO HP1200HT HU1100HW HX HY HZ1000NA NB NC ND NE900NF NG NH NJ NK800NL NM NN NO NP700NR NS NT NU600NW NX NY NZ OV500SC SD SE TA400SH SJ SK TF TG300SM SN SO SP TL TM200SR SS ST SU TQ TR1000SV SW SX SY SZ TV010020030010400500600

Reading contours and reliefUnderstanding the shape of the land by looking at a map isa very useful skill and can be essential if you’re going to bewalking in mountainous terrain. The height and shape ofthe land is shown on a map using ‘contour lines’. These linesappear as thin orange or brown lines with numbers on them.The number tells you the height above sea level of that line.A contour line is drawn between points of equal height, so anysingle contour line will be at the same height all the way alongits length. The height difference between separate contourlines is normally 10 metres, but it will be 5 metres in flatterareas. The map key will tell you the contour interval used.4030201030 4020 10The picture shown illustrates how a landscape can beconverted into contour lines on a map. An easy way tounderstand and visualise contour lines is to think of them ashigh tide lines that would be left by the sea. As the water leveldrops it would leave a line every 10 metres on the landscape.These marks would be contour lines.Being able to visualise the shape of the landscape by lookingat the contour lines of a map is a very useful skill that can bedeveloped with practice. It will allow you to choose the bestroute for your journey. When reading contour lines on a mapit’s helpful to remember the numbering on them reads uphill.It might be useful to imagine that to read contour line numbersyou have to be stood at the bottom of the hill looking up it,otherwise the numbers would be upside down. Other usefulthings to look out for when reading contour lines are rivers,which usually flow into valleys, or areas with very few contourlines, which will be flat.11

The picture below shows how contour lines can be used onmaps to describe different landscapes. Even though all thelines look similar at first, they are describing very differentlandscape features. The closer together the contour lines, thesteeper the slope of the hill. If a hill is very steep the contourlines might even merge into each other.A spur is a ‘V’-shaped hill that juts out. A simple way to tella valley from a spur when looking at contour lines is toremember that if the ‘V’ points uphill it’s a valley, if it pointsdownhill it’s a spur.Steep slopeSpurValleyShallow slope12