Maps are simply an accurate picture of the ground as seen from above, scaled down from life size, and with symbols to show particular features and landmarks. If you would like to learn how to plan your own routes, or move around with more confidence, follow our basic guide to map reading to get you started.
- On a 1:25 000 map, such as an OS Explorer, one unit of length on the map represents 25,000 units on the ground. So 1cm on the map represents 25,000cm or 250 metres on the ground. On a 1:50 000 map, 1cm on the map represents 500 metres on the ground.
- To find out what features the different symbols represent, for example buildings, different kinds of church, electricity pylons, roads and railways, woods, orchards, scrub or marsh and so on, consult the key shown on the map. The best way to learn these symbols is to relate them to the way they appear on the ground.
- Some map markings do not show up on the ground, such as council boundaries, contours and grid lines.
- Rights of way marked on maps will often be visible as a distinct path or track on the ground, but in less well-walked areas the path may not be visible. Footpaths and bridleways are marked as green dashes on OS Explorer maps and magenta on OS Landranger maps.
- Do remember that, although a good map will remain useful for at least a few years, the landscape is ever-changing and you should not be surprised if some features on the ground do not agree with your map.
Calculating distance and height
To measure the approximate distance of your route, take a piece of thin string and lay it carefully along the exact route on the map, then lay it straight along the scale line on the map’s margin. With practice, you’ll soon learn to estimate the distances involved by eye, but don’t forget the extra effort of climbing hills when calculating how long the route will take to walk.
Contours are lines connecting points of equal height above sea level that show the relief of the land. Together with spot heights, they portray the shape of the landscape, its height, the form taken by hills and valleys, the steepness of slopes, and so on. On OS Explorer maps, the interval between contours is five metres in lowland areas and 10 metres where mountainous. At random points along many of the contour lines a number is shown to indicate its height, always printed so that the top of the number points uphill. Every fifth contour line is printed more thickly than the others. The closer together contours are, the steeper the ascent or descent for the walker.
Spot heights – shown as a number beside a dot – appear at strategic points, including along roads where they level out at the top or foot of a hill. These can be a useful guide where there aren’t many contour height numbers.
All OS maps are criss-crossed by vertical and horizontal grid lines (coloured blue on OS Explorer maps) which are 4cm apart on 1:25,000 scale maps and 2cm apart on the 1:50,000 scale. A grid reference uses six figures to identify a particular spot on a map that is 100 metres square. The first three specify the vertical lines (the eastings) and the second three the horizontal (the northings).
So with the grid reference TQ303782, TQ indicates the 100 sq km of Britain designated by Ordnance Survey’s National Grid as ‘TQ’, and the location is 30 squares and three tenths east and 78 squares and two tenths north. Sometimes four-figure grid references are used to give a rough location that covers the map grid square, not a specific point within it.
How to take or locate a six-figure grid reference
What is the grid reference of the church in the example above?
- Identify the 1km square containing the church. Do this by selecting its left and bottom sides (imagine a letter ‘L’ bounds the square).
- Take the numbers on the edge of the map for these two sides (downstroke of the ‘L’ first, as you would write it). This gives: 31_25_ (Note: 3125 is the four-figure grid reference of the square).
- Now an extra figure must be added to each pair of numbers to specify to the nearest 100m where the church lies within the square. Estimate the number of tenths (100m) the church lies from the two sides, once again starting with the downstroke. It is seven tenths from the downstroke and four tenths from the horizontal stroke, so the 6-figure grid reference is: 317254.
To find a point on a map using a six-figure grid reference, simply do the reverse. Remember to start with the eastings (the first three figures) and then move up the northings (the last three). A helpful reminder is the saying: ‘go along the corridor and then up the stairs’.
Ordnance Survey has some useful guides to reading maps on their website: