OS history

Discover the history of Ordnance Survey


The name Ordnance Survey hints at how it all began.

Britain’s mapping agency has its roots in military strategy: mapping the Scottish Highlands following rebellion in 1745. Later, as the French Revolution rumbled on the other side of the English Channel, there were real fears the bloodshed might sweep across to our shores.

So the government ordered its defence ministry of the time – the Board of Ordnance – to begin a survey of England’s vulnerable southern coasts. Until then, maps had lacked the detail required for moving troops and planning campaigns.

It was an innovative young engineer called William Roy who was tasked with the initial small-scale military survey of Scotland.

Starting in 1747, it took eight years to complete what was known as the Great Map at a scale of 1:36 000 (1.75 inches to a mile). Roads, hills, rivers, types of land cover and settlements were recorded. William Roy described it as rather a ‘magnificent military sketch than a very accurate map of the country’.

Roy’s surveying parties of about eight relied on simple surveying compasses to measure the angles, and chains up to 50 feet long to measure distance between important features. Much of the rest was sketched in by eye. Nevertheless, the map was a powerful tool as part of a broader strategy to open up access to the Highlands.

The fact that Roy was just 21 years old with no military commission when he started the survey makes his achievements even more extraordinary. His work paved the way for modern surveying and he understood the strategic importance of accurate maps. At the time of his death in 1790 his vision of a national survey for Britain was almost within reach.

William Roy’s lifelong mission was to build a superior map of Britain, unparalleled in its accuracy. The day the Board of Ordnance set his suggested plan into action, Ordnance Survey was born. 

As surveyors carved our landscape into accurate triangles, the rest of Europe was in turmoil. Without good British maps the country couldn’t position its armies defensively.

The first maps were available to the public in the late Georgian era. These stunning ‘works of art’ weren’t cheap, but the owner was privy to a spectacular aerial view of the landscape until then only seen from a hot air balloon.

Almost the entire staff of Ordnance Survey was shipped across the Irish Sea to carry out a six inches to the mile survey of Ireland for accurate land taxation. England and Scotland soon followed in this new, powerful railway era. 

Accurate maps of all scales were more in demand, and new methods of mapmaking, including photography, made the process easier. 

In 1935, the Retriangulation of Great Britain began. Thousands of Trig Pillars were built on inhospitable peaks to serve as solid triangulation points. 

In peacetime again, Ordnance Survey was back to business as usual. A resurvey of larger towns and cities at the new scale of 1:1 250 corrected past inaccuracies and mapped wartime destruction. 

Under the direction of Vanessa Lawrence, OS saw a decade and a half of great change. OS MasterMap was launched; OS OpenData was made freely available and for the mobile generation, OS Maps was launched.

Today - and the future

OS has changed from a centuries-old venerable mapping company into a big data powerhouse. Our location data – or geographic information (GI) – has weaved itself into the very fabric of everyday life, right across Great Britain.

While the public still knows us for our comprehensive range of printed leisure maps, the digital side of the business accounts for more than 90% of turnover. The public and private sectors benefit from accurate information about ‘location’ and a world-leading reliable geographic framework helps deliver effective and efficient services.

The majority of information collected in Britain has some geographic feature – from the location of people, buildings and postcodes to administrative boundaries and flood risk areas. The potential to help make businesses more profitable and efficient through linking and analysing different sets of information is enormous.

Major investments have been made to help us collect and maintain richer data. This is achieved today through field surveyors, global navigation satellite systems, remote sensing and a range of advanced geographical information systems (GIS) tools and software.

All 243,241 square kilometres of Great Britain are surveyed and up to 20,000 changes are put into the database daily. By being at the forefront of geospatial capability for more than 230 years, we’ve built a reputation as the world’s most trusted geospatial partner.

Find out more

Read our resources to find out more about the history of Ordnance Survey.

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