Welcome to OS Explorer Maps...

A Brief History of the Ordnance Survey

The Board of Ordnance was formed when the Royal Arsenal was established in the Tower of London and is one of the oldest institutions in the country. It was financed by a separate vote from Parliament and was a Civilian body. The Board's powers were defined as "Custodian of the Lands, Depots and Forts required for the Defence of the Realm, and the Supplier of Munitions and Equiptment to the Army and Navy."

During the 18th Century, Britain had fallen behind in map making and this deficiency was highlighted by complaints from the Army during the 1745 Rebellion in Scotland. In response to these complaints, The Board of Ordnance was instructed to carry out a "Trigonometrical Survey" of the country.

The Very First OS Map

Early results were not of sufficient accuracy for making useful maps and it was not until 1787 that a "Great Base" of sufficient accuracy from which to commence triangulation was measured at Hounslow Heath.

This resulted in the publication of the first Ordnance Survey Map in 1801.

OS Maps in the 20th Century...

The Ordnance Survey saw great advances in the 20th Century:

• After the First World War, Colonel Charles Close developed a marketing strategy using covers designed by Ellis Martin to increase sales in the leisure market.
• In 1920 O. G. S. Crawford was appointed Archaeology Officer and played a prominent role in developing the use of aerial photography to deepen understanding of archaeology.
• In 1935, the Davidson Committee was established to review Ordnance Survey's future. The new Director General, Major-General Malcolm MacLeod, started the retriangulation of Great Britain, a task involving erecting concrete triangulation pillars on prominent hilltops throughout Great Britain.
• The national grid reference system was launched, with the metre as its unit of measurement.
• An experimental 1:25000 scale map was introduced. The one-inch maps remained for almost forty years before being superseded by the 1:50000 scale series, as proposed by William Roy more than two centuries earlier.
• In 1995, Ordnance Survey digitised the last of about 230,000 maps, making the United Kingdom the first country in the world to complete a programme of large-scale electronic mapping.
• The Ordnance Survey is now a civilian organisation with executive agency status.

The OS Explorer Series...

The OS Explorer series superseded the previous Pathfinder maps (which had green covers). The first experimental Explorer maps were published in 1994, with five titles issued simultaneously covering parts of the Chilterns, Mendips and Northumberland. On average the new maps covered three times the area of their predecessor Pathfinders, and were six times bigger than the blue-covered originals at this scale. Over the following two and a half years, a further 26 Explorer titles were published for different parts of the country, several introducing or developing ideas to test the usefulness of the new-look maps to the public.

As a result of the huge success of these early, experimental Explorer titles, the decision was taken in 1997 to cover the whole country with OS Explorer maps by 2003, adopting a common set of features and design elements for consistency. The series was completed in the six year period and now 403 different maps at the same 1:25 000 scale – each with a distinctive orange-coloured cover – chart every part of the country from the Shetland Islands in the north of Scotland to the Isles of Scilly off the Cornish coast.

The OS Explorer Series at a Glance....

• OS Explorer Maps are specifically designed for walkers and cyclists.
• They have orange covers, and contain 403 sheets covering the whole of Great Britain (the Isle of Man is excluded from this series).
• They are the most detailed leisure maps that Ordnance Survey publish and cover all types of footpaths and most details of the countryside for easy navigation.
• The OS Explorer maps, together with Outdoor Leisure, superseded the previous Pathfinder maps (green covers) which were numerous in their coverage of the country.