Ordnance Survey History

Ordnance Survey (OS) is an executive agency of the United Kingdom government. It is the national mapping agency for Great Britain, and one of the world’s largest producers of maps. The name reflects the original military purpose of the organisation (see ordnance and surveying) in mapping Britain during the Napoleonic Wars when there was a threat of invasion from France. OS is widely regarded[citation needed] as the most systematic and thorough mapping institution in the world, detailing every corner of Britain long before satellite technology made quality maps of the same standard available elsewhere in the world.


The roots of Ordnance Survey go back to 1747, when King George II 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. The survey was produced at a scale of 1 inch to 1000 yards. It was not until 1790 that the Board of Ordnance (a predecessor of part of the modern 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 began on mapping southern Great Britain using a baseline 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) 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.) 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 was completed in 1846.

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 came out in the mid-1830s, the Tithe Commutation Act 1836 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 at the Tower of London in 1841, OS 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 production but also to publish ‘facsimiles’ of National Manuscripts. Between 1861 and 1864 a ‘facsimile’ of the medieval Domesday Book was issued, county by county.

After the fire, OS relocated to a site in Southampton, and the twenty-five inch to the mile survey was completed by 1895.

Just under 400 towns with a population of over 4000 were surveyed at a scale of 1:500. Funding was agreed in 1855 and publication completed by 1895.

The 20th century

During the First World War, OS was involved in preparing maps of France and Belgium for its own use, and many more maps were created during World War II, including:

* 1:40000 map of Antwerp, Belgium
* 1:100000 map of Brussels, Belgium
* 1:5000000 map of South Africa
* 1:250000 map of Italy
* 1:50000 map of Northeast France
* 1:30000 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 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, 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 less than 32 times.

The Davidson Committee’s final report set OS on course for the twentieth century. 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.

OS had outgrown its site in the centre of Southampton (made worse by the bomb damage of the Second World War), and in 1969 moved to the suburb of Maybush, towards the edge of the city, where it remains today. Some of the remaining buildings of the original city-centre site are now used as part of the court complex.

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. OS is now a civilian organisation with executive agency status.

UK map range

Ordnance Survey maps are available in most bookshops, in a variety of scales:

* Route (1:625000) – Designed for long-distance road users. One double-sided map (dark blue cover) covers the whole of Great Britain.
* Road (1:250000) – Designed for road users. They have green covers; 8 sheets cover the whole of Great Britain.
* Tour or Tourist (c.1:100000 except Scotland) – One-sheet maps of area generally county-sized area, showing major and most minor roads and contains tourist information and selected footpaths. Larger scale maps are provided for major settlement centres. The Tourist map is similar, but only one sheet (Scotland) is available. The Tour map have sky-blue cover whereas the Scottish Tourist has pink covers adorned with symbols. There are 22 sheets (1-23, 12 being the previous Scottish sheet) of “Tour”.
* Landranger (1:50000) – 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.
* Explorer and Outdoor Leisure (1:25000) – Specifically designed for walkers and cyclists. They have orange covers, and the two series together contain 403 sheets covering the whole of Great Britain (the Isle of Man is excluded from this series). These are the most detailed maps that OS publish and covers all types of footpaths and most details of the countryside for easy navigation. The Outdoor Leisure series complement the Explorer, 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 Explorer maps, together with Outdoor Leisure, superseded the previous Pathfinder maps (green covers) which were numerous in their coverage of the country.

* Explorer Active (1:25000) – the Explorer maps are also available in a plastic-laminated waterproof version.
* Landranger Active (1:50000) – select Landranger maps are available in a plastic-laminated waterproof version, similar to the Explorer Active range. As of March 2008, 25 of the 204 Landranger maps were available as Landranger Active maps.

One series of historic maps[4] is a reprint of the OS first series from the mid 19th century, but re-scaled to 1:50000, re-projected to the Landranger projection, and given 1 km gridlines. This means that features from over 150 years ago fit exactly over their modern equivalents, and modern grid references can be given to old features.

Ordnance Survey also produces more detailed mapping at 1:10,000 and 1:1,250 scales, which is available from some of the more specialist outlets. This is produced to order from digital data, so the customer can choose exactly which area the map should cover.

The digitisation of the data has allowed OS to experiment with selling maps electronically. Several companies are now licensed to produce the popular scales (1:50000 and 1:25000) of map on CD/DVD or to make them available online for download. The buyer typically has the right to view the maps on a PC, a Laptop and a pocket PC/smartphone, and to print off any number of copies. The accompanying software is GPS-aware, and the maps are ready-calibrated. Thus, the user can quickly transfer a desired area from their PC to their laptop or smartphone, and go for a drive or walk with their position continually pinpointed on the screen. The price for an individual map is much dearer than the equivalent paper version, but the price per square km falls rapidly with the size of coverage bought. For instance, it is possible to buy a CD of 1:50000 (Landranger) mapping for all the national parks for less than £20, or a DVD of the whole of Britain (ie excluding Northern Ireland) for a little above £100. Explorer-scale maps are much more expensive.

British national grid reference system

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): short (approx 4 feet/1.2 m high), usually square, concrete or stone pillars 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 based on aerial photographs, but large numbers of the pillars remain.

OS still maintains a set of master geodetic reference points to tie the OS geographic datums to modern measurement systems including GPS. 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 1936–53.

OS MasterMap

Ordnance Survey’s flagship digital product, launched in November 2001, is OS MasterMap. This is a database that records every fixed feature of Great Britain larger than a few metres in one continuous digital map. Every feature is given a unique TOID (topographical identifier), a simple identifier that includes no semantic information. Typically each TOID is associated with a polygon that represents the area on the ground that the feature covers, in National Grid coordinates. MasterMap is offered in themed “layers”, for example, a road layer and a building layer, each linked to a number of TOIDs. Pricing of licenses to MasterMap data depends on the total area requested, the layers licensed, the number of TOIDs in the layers, and the period in years of the data usage.

MasterMap can be used to generate maps for a vast array of purposes, and maps can be printed from MasterMap data with detail equivalent to a traditional 1:1250 paper map.

OS claims that MasterMap data is never more than 6 months out of date, thanks to continuous review. The scale and detail of this mapping project is unique. Around 440 million TOIDs have so far been assigned, and the database stands at 600 gigabytes in size. MasterMap is currently (August 2005) at version 6.

OS is encouraging users of its old OS Landline data to migrate to MasterMap and in June 2007 announced a notice of withdrawal for this product as of 30 September 2008.

Geographical information science research

Since about 2001 Ordnance Survey has had a Research department that is very active in several areas of geographical information science, including:

* Spatial cognition
* Map Generalisation
* Spatial Data Modelling
* Remote sensing and analysis of remotely sensed data
* Semantics and ontologies

Ordnance Survey actively supports the academic research community through its External Research and University Liaison team. The Research department actively supports MSc and PhD students as well as engaging in collaborative research. Most Ordnance Survey products are available to UK Universities that have signed up to the Digimap agreement and data is also made available for research purposes that advances Ordnance Survey’s own research agenda.

More information can be found at Ordnance Survey Research

Access to data and criticisms

Ordnance Survey has been subject to criticisms. Most criticism centres on the point that OS possesses a virtual government monopoly on geographic data in the UK, while, although a government agency, since 1999 it has been required to act as a Trading Fund or commercial entity. This means that it is supposed to be totally self-funding from the commercial sale of its data and derived products – whilst at the same time it is supposed to be the public supplier of geographical information. In 1985 the “Committee of Enquiry into the Handling of Geographic Information” was set up in to “advise the Secretary of State for the Environment within two years on the future handling of geographic information in the UK, taking account of modern developments in information technology and market needs”. The Committee’s final report was published under the name of its chairman, Roger Chorley, in 1987. The report stressed the importance of widely available geographic information to the UK and recommended a loosening of government policies on distribution and cost recovery.

The Guardian newspaper has a long-running “Free Our Data” campaign, calling for the raw data gathered by OS (not to mention data gathered on its behalf by local authorities at public expense) to be made freely available for reuse by individuals and companies, as happens, for example, with such data in the USA, although the campaign rarely makes any comparison between the quality of the OS data and the quality of the data available from these free sources.

On the 7 April 2006 the Office of Public Sector Information (OPSI) received a complaint from the data management company Intelligent Addressing.[9] Many, although not all, complaints were upheld by the OPSI, one of the conclusions being that OS “is offering licence terms which unnecessarily restrict competition”. Negotiations between OS and interested parties are ongoing with regard to the issues raised by the OPSI report, OS being under no obligation to comply with the report’s recommendations.

Historical material

OS 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 currently provide historical mapping on ‘free’ terms, instead marketing commercially ‘enhanced’ reproductions in partnership with Landmark.

This can be contrasted with, for example, the approach in the Republic of Ireland in more recent times, where Ordnance Survey Ireland claims regular copyright over its mapping (and over digital copies of the public domain historical mapping).