The national mapping agency for the United Kingdom. They produce probably the finest and most detailed maps in the world. They are a British Government agency, but receive no funds from the Treasury.
History
18th Century
The Ordnance Survey has its origins in the 18th century, at a time when England was hard pressed by Jacobite rebellions in Scotland and war with France. In 1746, King George II ordered that a survey be made of the Scottish Highlands. This was carried out by William Roy, whose success led to the decision in 1790 for a survey of the southern coast of Britain to be made by the Board of Ordnance - hence the name. This survey was to be carried out because these coasts were vulnerable, and it was feared that the French Revolution might grip Britain.
In 1791, surveyors began to map the southern coasts at a scale of one inch to one mile. This work used a baseline established by Roy, without which the maps might never have been made. He can truly be seen as a father of the Survey. The first maps of this area were published in 1801. They were well received, and within twenty years, about a third of England and Wales had been mapped at this scale.
19th Century
In 1824, Major Thomas Colby - erstwhile Director of the Survey - and most of his team were ordered to Ireland to do a detailed six inch to one mile valuation survey. Colby established many methods of mapping for this work which would stand a long time after his death - designing specialist measuring equipment and establishing a systematic method for collection of place names.
The first six-inch maps of Ireland appeared in the 1830's, just as the Tithe Commutation Act increased demand for similarly detailed maps of England and Wales. Also, the growing prevalence of railways meant that more detailed maps were needed for railway engineers. It was this, along with the fact that some areas still remained unmapped, which caused the Treasury in 1840 to commission the six-inch mapping of remaining areas.
However, to perform this work, the Survey required access to more land. With the passing of the Ordnance Survey act in 1841, they were given the right to 'enter into and upon any land' for surveying purposes.
At that time, the Ordnance Survey's offices were situated at the Tower of London. When a fire broke out in the Grand Storehouse and threatened to destroy all their equipment and records, it was realised that a change of offices was in order. The Survey therefore moved to Southampton soon after the event.
In 1863, the scales at which the Survey should map were set. These were: six inches to the mile for 'mountain and moorland' and twenty five inches to the mile for rural areas. The one-inch maps were kept also, and work started on more detailed plans - as much as ten feet to one mile - for built up areas.
By 1895, the 25 inch survey had been completed. At the turn of the century, the Survey was planning an expansion of its business to capitolise on the expanding tourist industry. However, with the advent of the Great War, they were required to aid in the mapping of trenches and battlefields. It was at this time that aerial photography was first used for mapping purposes.
20th Century
After the war, the Ordnance Survey was under review and its future being discussed. Under a new director - Major-General Malcolm MacLeod - the retriangulation of Britain was begun, beginning with a new scale, 1:25000. After a few years, the 1:50000 scale was introduced as well. After the Second World War, this effort continued, along with the metrication of the maps.
The Ordnance Survey Today
Today, all of the Ordnance Survey's maps are digitised, and many companies use this data for their work. The example which the Survey is most proud of is Domino's Pizza's delivery system. Aerial photography and computerised 3D modelling are used for greater accuracy in map production, although the Survey's most popular product by far is its range of 1:50000 maps, a scale first suggested by William Roy more than 200 years ago.
Source: http://www.ordsvy.gov.uk