The Ordnance Survey is a British government body which serves as the national mapping agency for Great Britain and for the Isle of Man, producing a wide variety of maps for government and private purposes. In Northern Ireland, the same task is undertaken by the Ordnance Survey of Northern Ireland.
The Ordnance Survey is an executive agency and non-ministerial government department.
The agency's name reflects its creation together with the original military purpose of the organisation; ordnance and surveying following many centuries of civil and external conflict, reaching particular purpose during the Napoleonic Wars when there was a threat of invasion from France and maps of the coastal regions were required for defence planning; its logo includes the War Department's broad arrow heraldic mark. The Ordnance Survey is now a civilian organisation.
Ordnance Survey mapping today is usually classified as 'large scale' (which is to say showing more detail) or 'small scale'. Large-scale mapping comprises maps at 1:10 000 and larger, which mapping today is usually provided in digital format. Small-scale mapping comprises maps at smaller than 1:10 000 and includes the "leisure maps", such as the popular 1:50 000 Landranger series and 1:25 000 Explorer series.
The roots of Ordnance Survey go back to 1747, when Lieutenant-Colonel David Watson proposed the compilation of a map of the Scottish Highlands to facilitate keeping the rebellious clans down following the defeat of the Jacobite rising of 1745. In response, King George II commissioned a military survey of the Highlands, and Watson was placed in charge under the command of the Duke of Cumberland. Among his assistants were William Roy, Paul Sandby, and John Manson. The survey was produced at a scale of 1 inch to 1000 yards. The labours of Watson and Roy, in particular, resulted in The Duke of Cumberland's Map, now in the British Library.
Roy would go on to have an illustrious career in the Royal Engineers, and he was largely responsible for the British share of the work in determining the relative positions of the French and British royal observatories. This work was the starting point of the Principal Triangulation of Great Britain (1783 – 1853), and led to the creation of the Ordnance Survey itself. Roy's technical skills and leadership set the high standard for which Ordnance Survey became known. Work was begun in earnest in 1790 under Roy's supervision, when the Board of Ordnance began a national military survey starting with the south coast of England.
By 1791, the Board received the newer Ramsden theodolite (an improved successor to the one that Roy had used in 1784), and work began on mapping southern Great Britain using 5 mile baseline on Hounslow Heath that Roy himself had previously measured and that crosses the present Heathrow Airport. A set of postage stamps, featuring maps of the Kentish village of Hamstreet, was issued in 1991 to mark the bicentenary.
In 1801, the first one-inch-to-the-mile (1:63,360 scale) map was published, detailing the county of Kent, with Essex following shortly after. The Kent map was published privately and stopped at the county border while the Essex maps were published by Ordnance Survey and ignore the county border, setting the trend for future Ordnance Survey maps.
During the next twenty years, roughly a third of England and Wales was mapped at the same scale (see Principal Triangulation of Great Britain) under the direction of William Mudge, as other military matters took precedence. It took till 1823 to re-establish a relationship with the French survey made by Roy in 1787. By 1810, one inch to the mile maps of most of the south of England were completed, but were withdrawn from sale between 1811 and 1816 because of security fears. It was gruelling work: Major Thomas Colby, later the longest serving Director General of 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-inches-to-the-mile (1:10,560) valuation survey. The survey of Ireland, county by county, was completed in 1846. The suspicions and tensions it caused in rural Ireland are the subject of Brian Friel's play Translations.
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.
The British Geological Survey was founded in 1835 as the Ordnance Geological Survey, under Henry De la Beche and remained a branch of the Ordnance Survey until 1965. At the same time the uneven quality of the English and Scottish maps was being improved by engravers under Benjamin Baker. By the time Colby retired in 1846, the completion of six inch maps of Ireland was complete. This had led to a demand for similar treatment in England and work was proceeding on extending the six inch map to northern England, but only a three inch scale for most of Scotland.
When Colby retired he recommended William Yolland as his successor, but he was considered too young and a less experienced Lewis Hall was appointed instead. When after a fire in the Tower of London, the headquarters of the survey was moved to Southampton, Yolland was put in charge, but Hall sent him off to Ireland so that he was again passed over when Hall left in 1854 in favour of Major Henry James. Hall was enthusiastic about extending the survey of the north of England to a scale of 1:2,500. In 1855, the Board of Ordnance was abolished and the Ordnance Survey was placed under the War Office together with the Topographical Survey and the Depot of Military Knowledge. Eventually in 1870 it was transferred to the Office of Works.
The primary triangulation of the United Kingdom of Roy, Mudge and Yolland was completed by 1841, but was greatly improved by Alexander Ross Clarke who completed a new survey based on Airy's spheroid in 1858, completing the Principal Triangulation. The following year he completed an initial levelling of the country.
The Great Britain 'County Series'
After the first Ireland maps came out in the mid-1830s, the Tithe Commutation Act 1836 led to calls for a similar six-inch to the mile survey in England and Wales. Official procrastination followed, but the development of the railways added to pressure that resulted in the Ordnance Survey Act 1841. This granted a right to enter property for the purpose of the survey. Following a fire at its headquarters at the Tower of London in 1841  the Ordnance Survey relocated to a site in Southampton and was in disarray for several years, with arguments about which scales to use. Major-General Sir Henry James was by then Director General, and he saw how photography could be used to make maps of various scales cheaply and easily. He developed and exploited photozincography, not only to reduce the costs of map-making but also to publish facsimiles of nationally important manuscripts. Between 1861 and 1864, a facsimile of the Domesday Book was issued, county by county, and in 1870 a facsimile of the Gough Map.
From the 1840s the Ordnance Survey concentrated on the Great Britain 'County Series', modelled on the earlier Ireland survey. A start was made on mapping the whole country, county by county, at six inches to the mile (1:10,560). From 1854, to meet requirements for greater detail, including land-parcel numbers in rural areas and accompanying information, cultivated and inhabited areas were mapped at 1:2500 (25.344 inches to the mile), at first parish by parish, with blank space beyond the parish boundary, and later continuously. Early copies of the 1:2500s were available hand-coloured. Up to 1879, the 1:2500s were accompanied by Books of Reference or "area books" that gave acreages and land-use information for land-parcel numbers. After 1879, land-use information was dropped from these area books; after the mid-1880s, the books themselves were dropped and acreages were printed instead on the maps. After 1854, the six-inch maps and their revisions were based on the "twenty-five inch" maps and theirs. The six-inch sheets covered an area of six by four miles on the ground; the "twenty-five inch" sheets an area of one by one and a half. One square inch on the "twenty-five inch" maps was roughly equal to an acre on the ground. In later editions the six-inch sheets were published in "quarters" (NW,NE,SW,SE), each covering an area of three by two miles on the ground. The first edition of the two scales was completed by the 1890s. A second edition (or "first revision") was begun in 1891 and completed just before the First World War. From 1907 till the early 1940s, a third edition (or "second revision") was begun but never completed: only areas with significant changes on the ground were revised, many two or three times.
Meanwhile funding had been agreed in the 1850s for a more detailed survey of towns and cities. From 1850-53, twenty-nine towns were mapped at 1:528 (10 feet to the mile). From 1855 1:500 (10.56 feet to the mile) became the preferred scale. London and some seventy other towns (mainly in the north) were already being mapped at 1:1056 (5 feet to the mile). Just under 400 towns with a population of over 4000 were surveyed at one of these three scales, most at 1:500. Publication of the town plans was completed by 1895. The London first edition was completed and published in 326 sheets in the 1860s-70s; a second edition of 759 sheets was completed and brought out in the early 1890s; further revisions (incomplete coverage of London) followed between 1906 and 1937. Very few other towns and cities saw a second edition of the town plans.
From 1911 onwards (mainly 1911-1913), the Ordnance Survey photo-enlarged to 1:1250 (50.688 inches to the mile) many 1:2500 sheets covering built-up areas, for Land Valuation / Inland Revenue purposes. About a quarter of these 1:1250s were marked "Partially revised 1912/13". In areas where there were no further 1:2500s, these partially revised "fifty inch" sheets represent the last large-scale revision (larger than six-inch) of the County Series. The County Series mapping was superseded by the Ordnance Survey National Grid 1:1250s, 1:2500s and 1:10,560s after the Second World War.
From the late 19th century to the early 1940s, for War Office purposes, the OS produced many "restricted" versions of the County Series maps and other War Department sheets, in a variety of large scales, that included details of military significance, such as dockyards, naval installations, fortifications, and military camps. These areas were left blank or incomplete on standard maps - though for a brief period in the early 1930s, during the Disarmament talks, some of the blanks were filled in. The War Department 1:2500s, unlike the standard issue, were contoured. The de-classified sheets have now been deposited in some of the Copyright Libraries, helping to complete the map-picture of pre-War Britain.
The 20th century
During the First World War, Ordnance Survey was involved in preparing maps of France and Belgium for its own use, and many more maps were created during Second World War, including:
- 1:40000 scale map of Antwerp, Belgium
- 1:100000 scale map of Brussels, Belgium
- 1:5000000 scale map of South Africa
- 1:250000 scale map of Italy
- 1:50000 scale map of Northeast France
- 1:30000 scale map of the Netherlands with manuscript outline of German Army occupation districts.
After the war, Colonel Charles Close, then Director General, developed a marketing strategy using covers designed by Ellis Martin to increase sales in the leisure market. In 1920 OGS 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, an immense task involving erecting concrete triangulation pillars (trig points) on prominent (often inaccessible) hilltops throughout Great Britain. These were intended to be infallibly constant positions for the theodolites during the many angle measurements, which were each repeated no fewer than 32 times.
The Davidson Committee's final report set Ordnance Survey on course for the twentieth century. The national grid reference system was launched, with the metre as its unit of measurement. An experimental 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, 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.
In summer 2010, the announcement was made that printing and warehouse operations were to be outsourced, ending over 200 years of in-house printing.
GB map range
Ordnance Survey produces a large variety of paper maps and digital mapping.
Ordnance Survey produces a wide variety of different material aimed at business users, such as utility companies and local authorities. The data is supplied by Ordnance Survey on optical media or increasingly, on the Internet. Maps and data can be downloaded by way of FTP or accessed 'on demand' via a web browser. Organisations using Ordnance Survey data have to purchase a licence to do so. Some of the main items available are:
- OS MasterMap - Ordnance Survey's most detailed mapping showing individual buildings and other features in a vector format. Every real-world object is assigned a unique reference number (TOID) that allows customers to add this reference to their own databases. OS MasterMap consists of several 'layers', the main one being the Topography Layer but also available are aerial imagery, transport links and postcodes.
- OS VectorMap Local - a customisable vector dataset at 1:10 000 scale.
- OS Landplan - a raster map at 1:10 000 scale
- Meridian 2 and Strategi - mid-scale vector mapping.
- ADDRESS-POINT and Code-Point - Datasets with address information, allowing postcode searches of maps and so on. This is a joint venture with Royal Mail.
- Boundary-Line - Mapping showing administrative boundaries, such as counties, parishes and electoral wards.
- 1:10 000, 1:25 000, 1:50 000 and 1:250 000 Scale Raster - raster versions of the leisure maps at those scales.
- OS Street View - highly simplified mapping that focuses on showing streets and their names at the expense of other features.
- Land-Form PROFILE, PROFILE Plus and Panorama - these are digital terrain models.
OS's range of leisure maps are published in a variety of scales:
- Tour (1:100,000 scale except Scotland) – One-sheet maps covering a generally county-sized area, showing major and most minor roads and containing tourist information and selected footpaths. Tour maps are generally produced from enlargements of 1:250,000 mapping. Several larger scale town maps are provided on each sheet for major settlement centres. The Tour maps have sky-blue covers and there are now eight sheets in the series.
- OS Landranger map (1:50,000 scale) – The "general purpose" map. They have pink covers; 204 sheets cover the whole of Great Britain and the Isle of Man. The map shows all footpaths and the format is similar to that of Explorer, albeit with less detail.
- OS Landranger Active map (1:50,000 scale) – select OS Landranger maps are available in a plastic-laminated waterproof version, similar to the OS Explorer Active range.
- OS Explorer map and Outdoor Leisure (1:25,000 scale) – Specifically designed for walkers and cyclists. They have orange covers, and the two series together contain 403 sheets covering the whole of Great Britain. These 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 Outdoor Leisure series complement the OS Explorer Map, showing areas of greater interest in England and Wales (e.g. Lake District, Black Mountains) with an enlarged area coverage. It appears identical to the Explorer, except the numbering and a little yellow mark on the corner (relic of the old OL series). The OS Explorer maps, together with Outdoor Leisure, superseded the previous Pathfinder maps (green covers) which were numerous in their coverage of the country.
- OS Explorer Active map (1:25,000 scale) – the OS Explorer and Outdoor Leisure maps are also available in a plastic-laminated waterproof version.
Ordnance Survey also offers a print-on-demand service called 'OS Select'. This is printed to order from digital raster data, allowing the customer to choose exactly which area the map should cover. There is choice of two scales: 1:50,000 (area covered 40 km x 40 km) or 1:25,000 (area covered 20 km x 20 km).
Ordnance Survey also produces more detailed custom mapping at 1:10,000 (Landplan) and 1:1,250 or 1:500 (Siteplan), which is available from some of the more specialist outlets. Again, this is produced to order from Ordnance Survey large-scale digital data, and custom scales can also be produced by enlargement or reduction of existing scales.
Ordnance Survey produces maps for educational use, which are faithful reprints of old Ordnance Survey maps dating from the early 1970s to the early 1990s (estimated). These maps are widely seen in British schools and schools in the Commonwealth, as stand-alone geographic aids or sold as part of geography workbooks and/or textbooks.
From the early 2000s, Ordnance Survey offered a free OS Explorer Map to every 11-year-old in UK primary education in an attempt to increase school children's awareness of maps. By the end of 2010 when the scheme closes, over 6.4 million maps will have been given away. In place of the Free maps for 11-year-olds scheme, all schools that were eligible to receive free maps will have free access to the Digimap for Schools service provided by EDINA. This service is available to all schools, though those who are not eligible for free maps have to pay "a modest annual fee".
With the trend away from paper maps towards geographical information systems (GIS), Ordnance Survey has been looking into ways of ensuring schoolchildren are made aware of the benefits of GIS and has launched an interactive website aimed at children called 'MapZone' that features map-related games and learning resources. Ordnance Survey publishes a quarterly journal aimed at geography teachers called 'Mapping News'.
The original maps were made by triangulation. For the second survey, in 1934, this process was used again, and resulted in the building of many triangulation pillars (trig points): usually a four-foot square, concrete or stone pillar, erected at prominent locations such as hill tops. Their precise locations were determined by triangulation, and the details in between were then filled in with less precise methods.
Modern Ordnance Survey maps are largely based on aerial photographs, but large numbers of the pillars remain, many of them adopted by private land owners. Ordnance Survey still has a team of surveyors across Great Britain who visit in person and survey areas that cannot be surveyed using photogrammetric methods (such as land obscured by vegetation) and there is an aim of ensuring that any major feature (such as a new motorway or large housing development) is surveyed within six months of its construction. While original survey methods were largely manual, the current surveying task is simplified by the use of GPS technology. Ordnance Survey is responsible for a UK-wide network of GPS stations, known as OS Net. These are used for surveying but other organisations can purchase the right to utilise the network for their own uses.
Ordnance Survey still maintains a set of master geodetic reference points to tie each Ordnance Survey geographic datum to modern measurement systems including GPS.
Ordnance Survey maps of Great Britain do not use latitude and longitude to indicate position but a grid; the National Grid, which was introduced after the retriangulation of 1936–53.
Ordnance Survey historical works are generally available, as the agency is covered by Crown Copyright: works more than fifty years old, including historic surveys of Britain and Ireland and much of the New Popular Edition, are in the public domain. However, finding suitable originals remains an issue as Ordnance Survey does not provide historical mapping on 'free' terms, instead marketing commercially 'enhanced' versions in partnership with Landmark.
- Ordnance Survey
- National GPS network information: A guide to coordinate systems in Great Britain
- Royal Engineers Museum - Survey - origins of the Ordnance Survey
- Royal Engineers Museum - General Roy - Biography
- FieldenMaps.info - information on the history of Ordnance Survey maps
- Scans of the OS Popular Edition - England and Wales (1920-30s)
- Scans of the OS New Popular Edition - England and Wales (1940-50s)
- Ordnance Survey YouTube channel
- Porter, Whitworth (1889). History of the Corps of Royal Engineers. I. London: Longmans, Green, and Co. pp. 167–68. http://books.google.com/?id=lqlBAAAAIAAJ. Retrieved 2008-08-14
- Hindle, Paul (1998). Maps for Historians. Phillimore & Co. pp. 114–115. ISBN 0850339340.
- Hindle, Paul (1998). Maps for Historians. Phillimore & Co. pp. 117. ISBN 0850339340.
- "A brief history of Ordnance Survey". http://www.ordnancesurvey.co.uk/oswebsite/aboutus/history/index.html. Retrieved 2010-01-09.
- Seymour 1980, p. 139
- "Key dates". London Fire Brigade. Archived from the original on 2008-06-18. http://web.archive.org/web/20080618055617/http://www.london-fire.gov.uk/about_us/our_history/key_dates.asp.
- Harley, J. B., Ordnance Survey Maps: a descriptive manual, O.S. Southampton, 1975
- Oliver, Richard, Ordnance Survey Maps: a concise guide for historians (London 2005), pp.35, 54
- Oliver, Richard, and Hellyer, Roger, Ordnance Survey of Great Britain: Indexes to the 1:2500 and six-inch scales, David Archer, Newtown, Montgomeryshire, 2002
- Margary, Harry (1992). Old Series Ordnance Survey Maps of England and Wales. Unknown. ISBN 0-903541-01-7.
- "Official Homepage". Official Homepage. http://www.ordnancesurvey.co.uk. Retrieved September 29, 2005.
- "History of Cartography". Academic research by the University of Exeter. http://www.ex.ac.uk/geography/research/maphist.html. Retrieved September 29, 2005.