The Ordnance Survey takes its name from the Office of Ordnance and its title is a clear reflection of the military imperative that lay behind its formation. This was a gradual process. By the reign of Charles I officers of the Works had ceased to be directly concerned with the maintenance of military works and it became more usual for commissioners to be appointed consisting of military commanders, engineers and ordnance officers to survey military fortifications. As the 17th century progressed surveying and draughting was undertaken principally by royally-appointed engineers.
It was not until the late 17th and early 18th century, though, that the Office of Ordnance began to play a much greater role in the design and maintenance of fortifications. At the beginning of the reign of George I, in early 1716, work began to convert the top floor of the eastern annexe of the White Tower at the Tower of London into permanent accommodation for the newly created Ordnance Drawing Room. The first Ordnance Office draughtsman was Robert Whitehand who was appointed in 1712. Other staff were subsequently recruited including Clement Lemprière who was based at the Tower for almost forty years and is responsible for producing some of the earliest plans and drawings of the site and its buildings. On his death in 1746 the Drawing Room had a staff of six.
The Ordnance Survey, as its name suggests, has its origins in the Ordnance Office. After the Jacobite uprising of 1745, George II commissioned a detailed map of the Highlands to facilitate planning campaign strategies against the Highland clans. This led to a rapid increase in the Drawing Room establishment and by the early 1780s its staff numbered fifty.
The formation of the modern day Ordnance Survey, however, owes much to the earlier advocacy of Major General William Roy. As a young man, in the wake of the Jacobite Rebellion of 1745, he had been responsible for the production of a military map of Scotland. The pacification of Scotland by the Duke of Cumberland had highlighted the shortcomings of available mapping. Roy produced a map on the scale of 1 inch to 1000 yards. He was later commissioned by the Royal Society with the support of George III to measure a base line on Hounslow Heath and to link up with the Royal Observatory at Greenwich and Paris by triangulation. Triangulation forms the basis upon which modern scientific survey is built. For this project he used a theodolite built by one of the leading instrument makers of the day, Jesse Ramsden.
With the threat of invasion from France in the late 18th century the Board of Ordnance began to produce similar maps of other parts of Britain. In 1791 the Master-General of the Ordnance was given the task of establishing a controlled survey of the country. A Corps of Military Surveyors based at the Tower was also established during the same decade. It was these developments which ultimately resulted in the creation of the Ordnance Survey. Although their headquarters were originally in the Tower of London, after the 1841 Grand Storehouse fire the Ordnance Survey was formally established as a separate organisation and relocated to new premises in Southampton where it remains to this day. Although the original maps were created for military use, by the late 19th century the emergence of the idea of ‘productive leisure’ sparked growing interest in them by the general public. The Ordnance Survey continues today to produce maps for various military and civilian purposes.
Dr. Malcolm Mercer
Curator of Tower History
Ordnance Survey 1791-1991 (Ordnance Survey, 1991)
G Close, The Early Years of the Ordnance Survey (David & Charles, Newton Abbot, new edn, with introduction by J B Harley, 1969)
E Impey & G Parnell, The Tower of London: The Official Illustrated History (London, 2000)
R Hewitt, Map of a Nation: A Biography of the Ordnance Survey (London, 2011)
Wrought iron does not rust as quickly as cast iron. At Fort Nelson the Boxted Bombard, a large medieval cannon made of wrought iron is still in good condition despite being left outdoors and unprotected for hundreds of years.