Introduction to Map Reading with OS Maps

The basic elements of a map are made up of gridlines, contours and symbols. These elements can help you navigate, calculate distance and assess the elevation of the terrain as you hike.


Gridlines are lines that run horizontally across and vertically up a map. The horizontal lines are read left to right and are called ‘eastings’ while the vertical lines are read bottom to top and are called ‘northings’. Along these gridlines, at the bottom and side of the map, are numbers which allow you to get your grid references. To get the grid reference of any given point of a map you first work left to right along the eastings until you reach the lower left corner of the column of squares you are in. This will then give you a number. You then work up the northings until you get to the lower left corner of the row of squares you are in. This will provide you with another number. These numbers together provide you with the grid reference for your chosen location. You can also add in the National Grid code, a 2 letter code which is in essence the name of your map, before the numbers for a full grid reference.


Contours are the lines on a map that show us valleys, slopes, hills and mountains. They form rings around areas which change in elevation and usually move up in elevation in multiples of 5 metres. When the elevation is extreme, as with mountainous regions, they sometimes move up in multiples of 10. As shown below, a series of rings can give you the elevation of any given point on a map. Where the rings are closer together it means that the climb is steeper and where they are further apart means that the elevation is more gradual.


Symbols are used on maps to denote different buildings and points of interest on the mapped regions. As well as providing a simple way to categorise these places, symbols also provide a visual, rather than textual, way to quickly learn information about a place. These buildings and points of interest can then be used to find your position on a map. All symbols are explained on a key found on the map.

Plotting a Route

Plotting your route is an essential part of planning a hiking trip. You may have written guides, and the way may be well sign posted, but it is always important to have a mapped route ready for when you need it most. If you’re following a specific route you can prepare by looking at the elevation, the landmarks and the distance along your route. The elevation and landmarks will help you choose the best path from A to B and the distance will help inform you how far you can hope to travel on your trip. To calculate distance you can use a piece of string to follow your route on the map, winding or a straight line, then measure this piece of string. The measurement of this string can then give you the distance of your route when compared against the distance key at the bottom of your map.

Using an OS GPS Device

Ordnance survey also produce GPS devices such as the OS Aventura. Although your location, distance, altitude and bearing are all provided by the technology within the Aventura, a lot of the principles of Map reading will still apply and are still necessary.

Learning the basics of map reading will allow you to look ahead on your route and make judgements about ascent difficulty via contours. It’s also vital to understand scale and symbols within your digital maps, these are consistent across digital and hard copy OS Maps.


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