OS Maps: Scale, Distance and Direction

The scale number on an OS map indicates how many centimetres on the ground are represented by a centimetre on the map. On a 1:100,000 scale map, one centimetre on the map represents 100,000 cm on the ground, in other words, one centimetre on the map represents one kilometre in reality. A scale of 1:5,000 therefore means that a centimetre on the map represents a distance in real life of 5,000 centimetres (50 metres). This method of representing the scale of a map is called the fractional method, but you will also see graphical representations or written representations like 2 cm = 1 km.

Ordnance Survey maps are printed with north at the top. East is therefore to the right, south to the bottom and west to the left. The four points north, east, south and west are called the cardinal points of the compass. There are four other directions exactly half-way between the cardinal points - north-east, south-east, south-west and north-west. These are often abbreviated to NE, SE, SW and NW. Between these and the cardinal points, there are eight others, each beginning with the closest cardinal point e.g. the direction between north and north-east is called north-north-east. Using these descriptions for a direction is usually sufficient unless you are trying to navigate in difficult terrain. Then you need to use exact compass bearings. North is a bearing of zero degrees, east is ninety degrees, south is one hundred and eighty degrees and west is two hundred and seventy degrees. If you were required to follow a bearing of thirty degrees, you would be travelling in a direction somewhere between NNE and NE.