OS history

In 1784, Roy was commissioned by the Royal Society to geodetically connect the Royal Observatories of Greenwich and Paris to solve a dispute over their relative positions. To do this he needed a more sophisticated theodolite (a precision instrument for measuring angles horizontally and vertically) than had previously existed.

This could only be created by Jesse Ramsden, the leading instrument maker of the day. He produced a spectacular Great Theodolite, three years in the making, measuring three feet across.

To begin the London/Paris triangulation, it was necessary to measure a baseline that Roy established on the flattest suitable ground on Hounslow Heath (a line that now crosses Heathrow airport).

Using the Ramsden theodolite and trigonometry, a network of accurately measured triangles was extended to France and then back to a verification baseline in Kent.

Newspapers of the time lauded Roy as an ‘incomparable engineer’ while the Royal Society awarded him its highest accolade – the Copley Medal.

The five-mile line was to later form the basis of the Principal Triangulation of Great Britain.

In his lifetime, Roy had been convinced that ‘the honour of the nation’ depended on creating ‘a map of the British islands’ that was ‘greatly superior in point and accuracy to any that is now extant’.

Transforming his vision into reality, the Board of Ordnance bought a second new (and improved) Ramsden theodolite.

The date was 21 June 1791 – officially recognised as the birth of Ordnance Survey.

To brace England for the threat of French invasion, the Board of Ordnance commanded the maps be fleshed out for tactical military purposes… starting with our vulnerable coastal areas.

It was Charles Lennox, third Duke of Richmond and Master-General of the Board of Ordnance who founded the Trigonometrical Survey for national defence purposes.

Without good British maps the country couldn’t position its armies defensively. It was crucial to map the features that could be hidden behind, aimed at and where troops could be quartered. It was also important to record the type of terrain.

The priority was to start mapping the coastal areas that were most vulnerable to invasion. Redundant warning beacons dotted along the coast made ideal trig points. It’s said that the light from the surveyors’ lamps was occasionally mistaken by locals as signals of French invasion.

Before summer 1794 had turned into autumn, mapmakers had ‘laid down’ the triangulation of the coast from Fairlight Head in Sussex to Portland in Dorset.

Mapmaking began attracting a lot of attention from landowners, who offered landmarks in their own estates as secondary trig points.

The surveyors otherwise often built small stacks of stones to indicate where their theodolite had been placed and these remained in the landscape for months afterwards.

Once peace was established, the progress of map publication often depended on enough landowners in an area agreeing to buy maps in advance.

‘Ordnance Survey’ wasn’t used at all until 1801 when its director wrote it on a draft document. The name wasn’t printed on a map until the 1810 ‘Ordnance Survey of the Isle of Wight and part of Hampshire’.

The first Ordnance Survey map was published in 1801. England’s most south-easterly county, Kent, was one area most vulnerable to French invasion.

These early maps, with their elaborate hill shading and attention to communication routes, highlight the emphasis given to military use. In time, this military face would soften and the map design was developed to appeal to a much wider audience.

Triangulation was used as an accurate framework to the internal mapping which was beautifully intricate. Maps were made by first breaking down the great triangles into smaller ones.

Surveyors then used several techniques to create ‘intersected points’ to provide a framework for the map detail. Place names often proved difficult as locals could argue over what name was actually correct.

Eventually a Name Book system was put in place. Variations of all proper names such as rivers and hills, as well as towns, were recorded in a series of books and from this selection the most authoritative was chosen for publication.

This first map took three years to complete, and surveyors worked to a scale of two inches to one mile, that was reduced to one inch to a mile when printed.

Maps were engraved ‘in reverse’ on copper plate which was used for printing. Separate legends appeared for the symbols – the maps were huge enough without them.

Its launch was much anticipated, and the public could buy Ordnance Survey maps either from the Board of Ordnance headquarters in the Tower of London, or from William Faden, a map seller at Charing Cross.

The first maps were sold at three guineas (£3 3s) per county survey, which was between one and three weeks’ wages for the average person.

Part of their appeal was they offered a bird’s eye view of the landscape – until then only the privilege of very few hot air balloonists.

Four years later, a map of Essex followed. Within 20 years, about a third of England and Wales had been mapped at the one inch scale under the direction of William Mudge.

It was thought that 50 years would be long enough to map the country, but the entire first series of maps wasn’t published until 1870.

Staff could now legally tread upon any land for surveying purposes, and a fire in Ordnance Survey’s Tower of London offices saw the headquarters move to Southampton.

In 1824, Parliament ordered Colby and his staff across the Irish Sea. A six inches to the mile accurate map of Ireland was needed for land taxation purposes.

An utter perfectionist, Colby commissioned specialist measuring equipment, established a systematic collection of place names and re-organised the map-making process to produce clear, accurate plans.

He believed in sharing the hardships as well as the achievements of his staff.

After travelling with his men, he’d help to build camps, and arranged mountain-top feasts with huge plum puddings at the end of each surveying season.

The survey of Ireland was completed in 1846 and the maps are now an unrivalled resource for studying the period before the Great Irish Famine (1847-50).

Soon after the first Irish maps began to appear in the mid-1830s, there were calls for similar six-inch surveys in England and Wales. This was the era of railway mania and the one-inch map was virtually useless for the new breed of railway engineers.

Colby also introduced height to Ordnance Survey maps by commissioning a national geodetic levelling survey in relation to mean sea level in Liverpool measured using a tide gauge.

Now, surveyors needed greater access than ever before and so, in 1841, the Survey Act gave them a legal right to ‘enter into and upon any land… for the purposes of making and carrying out a survey’.

Yet 1841 was also the year Ordnance Survey’s cramped Tower of London offices were at the centre of a national catastrophe. Fire swept through the Grand Storehouse, threatening to engulf the Crown Jewels in the Martin Tower. Miraculously, the precious things were saved, and most of Ordnance Survey’s records and instruments were also carried to safety. But the fire highlighted the Survey’s desperate need for more office space, and prompted a move to a new Southampton headquarters in an empty former barrack building.

Yet the tide of history would soon sweep Ordnance Survey back to its roots. During the Great War, mapmakers were posted overseas and, under appalling conditions, made and printed millions of maps for the allies.

Amid reform, Victorians had a real need for accurate mapping and, after years of disagreements, several different scales of maps were agreed, including six inches to the mile for mountain and moorland, 25 inches to the mile for rural areas, right up to ten and a half feet to the mile for built-up areas.

Zincography (using zinc sheets) began to replace lithography (using stone) as a method of printing, with copper plate engravings still used for the one inch maps.

Photography was introduced to the map making process in 1855 by Sir Henry James. He was probably Ordnance Survey’s most egotistical Director General but he realised how maps could
be cheaply and quickly enlarged or reduced using this new science. He used an elaborate ‘glass house’ to develop prints using sunlight. He later claimed to have invented photozincography (a photographic method of producing printing plates) although it had been developed by two of his staff.

James welcomed international interest and made all inventions, mathematical tables and scientific data openly available, even publishing a book on the subject.

Colour map printing was introduced to the one-inch map in 1887 while in 1902, Ordnance Survey employed women for the first time, to mount and colour maps.

The 20th century brought more cyclists and motorists onto the roads and ramblers into the countryside. The new Director General, Colonel Charles Close (affectionately known as ‘Daddy’ to his staff) quickly saw there was potential for huge map sales among this expanding leisure market.

As Britain entered the First World War, staff from Ordnance Survey were posted overseas. Working in appalling conditions, surveyors plotted the lines of trenches and, for the first time, aerial photography was used to capture survey information.

By the end of the First World War, Ordnance Survey had printed 20 million maps for the war effort.

After the War, thoughts turned to marketing the maps to engage a new wave of outdoor enthusiasts. A professional artist was appointed to produce eye-catching covers for the one-inch maps.

Ellis Martin’s classic designs boosted sales to record levels, and maps were soon seen as essential by the general public.

When the Second World War broke out, focus turned to the military. A huge proportion of Ordnance Survey’s civilian staff were called up, and the Southampton HQ was bombed. By 1945, 342 million maps had been produced for the war effort. 

A whole raft of new legislation, and rapid development after the Great War, brought demands for accurate, up-to-date mapping.

In 1935 the Davidson Committee was set up to review Ordnance Survey’s future. That same year, Director General Malcolm MacLeod launched the Retriangulation of Great Britain.

Surveyors began the Olympian task, building the now-familiar concrete triangulation pillars on hilltops and mountains throughout Britain.

Most were made of cast concrete but a few were built from local stone cemented together.

Surveyors dragged heavy loads of materials over isolated land by lorry, packhorse and sheer brute force. They had to go down as much as 15 feet under the surface to secure them in place.

It was a rugged life for the surveyors with few home comforts. Wet clothing, frozen fingers and bleary eyes caused by long hours of observing were the order of the day (and night).

Around 6,500 Trig Pillars were put up in prominent positions around the country, and many remain in the landscape today. These shining white monoliths supported theodolites and were intervisible, with surveyors standing at one pillar to observe lights on others.

Ordnance Survey was set on course for the 20th Century. The metric national grid reference system was launched, together with the 1:25 000 scale series of maps.

Yet a darker period loomed as the Second World War broke out. A third of Ordnance Survey’s civilian staff was called up and its printing presses were kept busy with war production.

Not only that, its Southampton HQ was bombed and badly damaged. Staff were relocated to the Home Counties where they produced 1:25 000 scale maps of France, Italy, Germany and most of the rest of Europe in preparation for invasion.

Until the 1960s, all Director Generals held an army rank. In the event of a major war, Ordnance Survey would limit its civilian activities and concentrate on military work. The military appetite was insatiable: The Normandy Landings alone devoured 120 million maps, and a total of 342 million were produced for the entire war effort.

Then things moved on apace. The digital age began, and with it, the first computerised large-scale maps appeared. Ordnance Survey became a fully civilian and more commercial operation.

Post-war, work began on creating a new national map with urban areas surveyed at 1:1 250; rural at 1:2 500 and mountain and moorland at 1:10 000.

The National Grid system was now used on all Ordnance Survey maps to identify the position of any feature. It breaks Great Britain down into progressively smaller squares identified first by letters and then numbers and is still taught to all pupils in primary school today.

By 1962 the retriangulation of Britain was finally complete. Aerial surveying helped speed up the new ‘continuous revision’ strategy, and up-to-date drawing and printing techniques were introduced.

But the organisation was still fragmented, scattered across southern England in various buildings. All that changed in 1969 when the majority of Ordnance Survey’s 4,000-strong staff moved to a purpose-built head office at Maybush in Southampton. It was a cavernous building, as everything was produced and stored in-house. Surveyors were based in field offices around the country.

Photography became a dominant technology, both providing information for ground survey and for cartographic and printing processes. The company adapted a method of cutting away
detail from coated glass called ‘scribing’ to the use of plastic sheets which allowed map detail to be built up in layers.

Computers were used to simplify updating future map editions, and in 1971, digital mapping was introduced to large-scale map production. A year later, the first Outdoor Leisure Map – The Dark Peak – was published, while 1973 saw the production of the first large-scale digital map. This was, said Director General B St G Irwin, “…An event of the greatest possible importance in mapping.”

Electronics transformed surveying equipment. Light beam technology and automatic data recording equipment led to much faster data collection.

In 1974 the Ordnance Survey Director General position became a civilian post. The one-inch map was replaced by a metric 1:50 000 Landranger map. Popular areas of 1:25, 000 scale mapping were used to create Outdoor Leisure Maps, with the remainder of this national series called Pathfinder.

In 1983 the last military personnel left Ordnance Survey, making it a wholly civilian organisation. The War Department’s broad arrow remained in the Ordnance Survey Logo a further 21 years afterward, a nod to its military past.

In 1990 Ordnance Survey became an Executive Agency, and work began on the National Global Positioning Network to replace the triangulation network.

A year later, it celebrated its bicentenary with a reception in the Tower of London with HM the Queen and the Duke of Edinburgh. Commemorative postage stamps were issued in recognition
of two successful centuries.

In 1995, Ordnance Survey launched its website and 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. Computers further transformed the map-making process, with electronic data becoming routinely available to customers within 24 hours of being surveyed.

By the end of the 1990s, all field surveyors were using hand-held pen computers to record field measurements and transfer the results back to head office.

By the end of the millennium, the agency was designated a Trading Fund, required to cover its costs by charging for its products and give a proportion of its profits to the Treasury.

More products were launched, with innovative uses for mapping data which became available to more people than ever before. A brand new headquarters was officially opened in Southampton by the Duke of Edinburgh, and OS data underpinned the hugely successful London 2012 Olympic Games.

On 4 September 2000, Vanessa Lawrence was appointed as the first female Director General and Chief executive, forming another milestone in the organisation’s long history.

The following year, OS MasterMap was launched: an intelligent geospatial database offering definitive consistent and maintained referencing to more than 460 million man-made and natural landscape features in Britain.

Customers’ information could now be integrated into it, held as separate layers, or linked to other Ordnance Survey map products.

In April 2009 construction began on the new head office, Explorer House, at Adanac Park on the outskirts of Southampton. It was officially opened by Prince Philip, the Duke of Edinburgh, on 4 October 2011.

With the new building came the outsourcing of warehouse operations and the end of more than 200 years of in-house printing. Large-scale maps had not been printed at Ordnance Survey since geographical information systems became commonly available.

OS OpenData was made freely available for the first time in 2010, when 12 open data products were released. We have continued to update and add to OS OpenData, and in 2015 we released OS Open Map – Local, OS Open Names, OS Open Rivers, and OS Open Roads. This was then followed by the release of OS Open Greenspace in 2017.

Over the first eight years of OS OpenData we saw data downloaded 1.9 million times. On average, 150 people download OS OpenData every day. That’s 54,750 people a year. Here is a quick trip through our open data journey highlighting some of the key milestones.

This is the era Ordnance Survey partnered up with Local Government Group in launching GeoPlace to create and maintain a single National Address Gazetteer.

As Great Britain cheered on its athletes during the London 2012 Olympic Games, OS data was underpinning the work of 42 organisations who pulled together to deliver this hugely successful event. 

For the mobile generation, OS Maps was launched. The premium mapping App from Ordnance Survey allowed users for the first time to view, navigate and download the most up-to-date OS Landranger and OS Explorer maps of Great Britain on mobile devices in high resolution.