__NOTOC__

The retriangulation of Great Britain was a triangulation project carried out between 1935 and 1962 that sought to improve the accuracy of maps made of

Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It i ...

. Data gathered from the retriangulation replaced data gathered during the Principal Triangulation of Great Britain, which had been performed between 1783 and 1851.

History

The retriangulation was begun in 1935 by the Director General of the

Ordnance Survey Ordnance Survey (OS) is the national mapping agency for Great Britain. The agency's name indicates its original military purpose (see ordnance and surveying), which was to map Scotland in the wake of the Jacobite rising of 1745. There was a ...

, Major-General Malcolm MacLeod. It was directed by the cartographer and mathematician

Martin Hotine Brigadier Martin Hotine CMG CBE (17 June 1898 – 12 November 1968) was the head of the Trigonometrical and Levelling Division of the Ordnance Survey responsible for the 26-year-long retriangulation of Great Britain (1936–1962) and was th ...

, head of the Trigonometrical and Levelling Division. A problem during the Principal Triangulation was that the exact locations of surveying stations were not always rediscoverable, relying on buried markers and unreliable local knowledge. To overcome this, a network of permanent surveying stations was built, most familiarly the concrete triangulation pillars (about 6,500 of them) found on many British Isles hill and mountain tops, but there were many other kinds of surveying stations used. To minimise differences between the 1783-1851 survey and the retriangulation, eleven Principal Triangulation stations from Dunnose on the

Isle of Wight The Isle of Wight ( ) is a Counties of England, county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the List of islands of England#Largest islands, largest and List of islands of England#Mo ...

Great Whernside Great Whernside is a fell in the Yorkshire Dales, England, not to be confused with Whernside, some to the west. Its summit is the highest point of the eastern flank of Wharfedale above Kettlewell. Great Whernside forms the watershed between ...

in Yorkshire were chosen and pillars erected on them to act as the core framework from which all other measurements were made. The main work of the Retriangulation was finished in 1962, creating the now familiar Ordnance Survey National Grid, with the system continuing to be used and measurements refined by ground-based surveying into the 1980s, after which satellite use took over. Electronic measuring devices were introduced towards the end of the Retriangulation, but at that time were not proven reliable enough to replace traditional surveying.

Notes and references

Bibliography

* * *{{cite book , year=1980 , editor-first=W. A. , editor-last=Seymour , title=A History of the Ordnance Survey , publisher=Dawson , location=Folkestone, England , isbn= 0-7129-0979-6 , url=https://books.google.com/books?id=PWkKAQAAIAAJ , oclc=654935343 , postscript = . Freely available online at th
Ordnance Survey, Seymour

External links

Daily Telegraph article about the retriangulation of Great BritainNational GPS NetworkInformation and Maps on many aspects of Trigangulation (& Levelling) in Great Britain
Angle Surveying of the United Kingdom Geography of Great Britain Geodetic surveys

History

Notes and references

Bibliography

See also

External links