The Ordnance Survey (OS) is now a civilian organisation and government agency in the United Kingdom, and one of the world's largest producers of maps. In addition to producing a wide range of maps of Great Britain1, the organisation is also working in over sixty countries world-wide.
The roots of the United Kingdom Ordnance Survey (OS) go back to 1747, when King George II of England commissioned a military survey of the Scottish highlands following the Jacobite revolt of 1745. William Roy was the engineer responsible for this pioneering work; one of the staff involved was noted artist Paul Sandby. It was not until 1790 that the Board of Ordnance (the predecessor of the Ministry of Defence) began a national military survey starting with the south coast of England in anticipation of a French invasion.
By 1791, the Board had purchased the new Ramsden theodolite, and work commenced on mapping southern Britain using a baseline that Roy himself had previously measured and which crosses the present Heathrow Airport. In 1801 the first one-inch map was published: it was of the county of Kent, with a second of Essex following shortly after.
During the next twenty years about a third of England and Wales was mapped at the one-inch scale. It was gruelling work: Major Thomas Colby , later the longest serving Director General of the Ordnance Survey, walked 586 miles in 22 days on a reconnaissance in 1819.
In 1824, Colby and most of his staff moved to Ireland, to work on a six inch to the mile valuation survey. Colby was not only involved in the design of specialist measuring equipment. He also established a systematic collection of place names, and reorganised the map-making process to produce clear, accurate plans. He believed in leading from the front, travelling with his men, helping to build camps, and as each survey session drew to a close arranging mountain-top parties with enormous plum puddings.
After the first Irish maps began to come out in the mid-1830s, the Tithe Commutation Act led to calls for similar six-inch surveys in England and Wales. After official prevarication, the development of the railways added to pressure that resulted in the 1841 Ordnance Survey Act. This granted a right to enter property for the purpose of the survey.
Following a fire at its headquarters in the Tower of London, the OS was in disarray for several years with arguments about which scales to use. Major-General Sir Henry James was now Director General, and he saw how photography could be used to make maps of various scales cheaply and easily. The twenty five inch to the mile survey was complete by 1895.
World War I
During the First World War the OS was more involved in preparing maps overseas, but after the war Colonel Charles Close , the current Director General, 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 Archeology Officer and played a prominent role in developing the use of aerial photography to deepen understanding of archaeology.
The Davidson Committee was established in 1935 to review the Ordnance Survey's future. The new Director General, Major-General Malcolm MacLeod , started the retriangulation of Great Britain, an immense task which involved erecting concrete triangulation pillars (trig points) on prominent hilltops throughout Britain.
The Davidson Committee's final report set the OS on course for the twentieth century. The national grid reference system was launched, with the metre as its measurement. An experimental new 1:25,000 scale map was introduced. The one-inch maps remained for almost forty years before being superseded by the 1:50,000 scale series, as proposed by William Roy more than two centuries earlier.
In 1995 the Ordnance Survey digitised the last of about 230,000 maps, making Britain the first country in the world to complete a programme of large-scale electronic mapping.
The OS is now a civilian organisation.
UK Map Range
Ordnance Survey maps are available in most bookshops, in a variety of scales:
- Route (1:625,000) - Designed for long-distance road users. One double-sided map (dark blue cover) covers the whole of the Great Britain.
- Road (1:250,000) - Designed for road users. They have green covers; 8 sheets cover the whole of the Great Britain.
- Landranger (1:50,000) - The "general purpose" map. They have pink covers; 204 sheets cover the whole of the Great Britain and the Isle of Man.
- Explorer (1:25,000) - Specifically designed for walkers and cyclists. They have orange covers; 470 sheets cover the whole of the Great Britain (but the Isle of Man is excluded from this series). Explorer maps have replaced two older series of 1:25,000 map:
- Outdoor Leisure - Also for walkers & cyclists. These 33 maps specifically covered tourist destinations. Identified by their yellow covers and often double-sided, they predate the explorer maps. They covered a larger area than Pathfinders.
- Pathfinder - Pathfinders were the predecessors to the Explorer series. These maps were smaller than the new ones and generally had no overlap between adjacent sheets, making them less convenient to use. Some Pathfinder were phased out by the arrival of Outdoor Leisure maps, the remainder were later replaced by the new Explorer series.
Also produced are various historical and archealogical maps, and road maps of certain popular "tourist" areas, all at a variety of scales. The Ordnance Survey produce a free mapping index, showing which parts of the country are covered by which maps.
The original maps were made by building short (approx four foot high), square, concrete pillars on top of various high points and working out the exact position of these by triangulation. The details in between were then filled in with less precise methods. Modern Ordnance Survey maps are based on aerial photographs, but large numbers of the pillars, or trig points remain.
The OS still maintains a set of master geodetic reference points to tie the OS geographic datums to modern measurement systems including GPS.
Eastings and Northings
Main article: British national grid reference system.
The Ordnance Survey maps of Great Britain do not use latitude and longitude to indicate position but a special grid. The grid is technically known as OSGB36 ™ (Ordnance Survey Great Britain 1936), and was introduced after the retriangulation of 1936-1953.
The Ordnance Survey is currently undertaking an unprecedented project to map every fixed feature of Great Britain larger than a few metres in one continuous digital map . Every feature is given a unique topographical identifier or "toid", which also includes information about its type. For example, the height of a low bridge is encoded into its toid. The digital database this creates is never more than about 6 months out of date, and can be used to generate maps on any scale, for a vast array of purposes. The scale and detail of this mapping project is so far unique.
An external news article about this can be found here (Guardian Unlimited).
- Note that the Ordnance Survey deals only with maps of Great Britain (and to an extent, the Isle of Man). Northern Ireland, whilst an integral part of the United Kingdom, is mapped by a separate government agency, the Ordnance Survey of Northern Ireland .