You might have noticed by now that Ordnance Survey maps are covered in a series of blue grid lines. These grid lines help you to pinpoint an exact location anywhere on the map. The vertical lines are called 'eastings', as they increase in value as you travel east on the map. The horizontal lines are called 'northings' as they increase in value as you travel north on the map.
These are linked to the National Grid which provides a unique reference system, and can be applied to all OS maps of Great Britain, at all scales. Great Britain is covered by grid squares measuring 100 kilometres across and each grid square is identified by two letters.
Clyst Valley Regional Park is covered by three OS maps
1:25,000 Explorer 114 Exeter and the Exe valley
1:25,000 Explorer 115 Exmouth and Sidmouth
1:50,000 Landranger 192 Exeter and Sidmouth