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Making Maps: The Story of the UK’s Ordnance Survey

Just like high tea, the stiff upper lip and slowly dribbling rain, there is something quintessentially British about our topic today. Ask any man, woman or child up and down this small nation about maps, and it’s likely that one name will come up -The Ordnance Survey. 

Maps have become part and parcel of lives and not something we give too much thought to these days. Today, with Google maps we can examine parts of the globe in incredible detail whenever we want and we barely give a thought to how they are – or were created. We take it for granted that we can have up to date maps in a flash, but our story today involves not only the emergence of the Ordnance Survey but an extraordinary endeavour to map the entirety of the British Isles in detail that took decades to complete. 

Ordnance Survey 

Let’s begin with a quick overview of what the Ordnance Survey maps are because if you’re not British, it’s entirely likely that you’ve never heard of them. 

Things have changed considerably in the last couple of decades with the emergence of smartphones and their apps that have replaced many, dare I say, more old fashioned ways of doing things. But for the sake of this story, let’s go back to the early 2000s, a simpler time before rabid online bitterness became a global obsession.

I should probably also add before we continue, that the British love to ramble, a sedate walk through rural landscapes, preferably on a Sunday, and ideally with a country pub midway to stop in for a pint and a roast dinner. But the problem with walking in Britain, as I’m sure is the case in other countries, is that you are more often than not walking across somebody’s property. In some cases, under the wonderfully named ‘right to roam’ you are well within your legal right to walk across wild areas of Britain without needing to use a footpath. 

However, in the majority of cases, you are required to use paths that criss-cross the entire country. Some of these, known as the National Trails, are long-distance routes, while others simply connect rural villages by crossing farmland in between. 

And how do you know where these routes are? By consulting your trusty ordnance survey map of course. Nowadays, these maps are online, but not too long ago most self-respecting rambling households would have owned at least one fold up Ordnance Survey paper map – remember those – that gives information on a specific local area in extraordinary detail. Whether you’re looking for the site of an old Roman fort or simply a footpath between Lower Swell and Upper Slaughter – and yes these are real places – then the Ordnance Survey maps were exactly what you were looking for. 

The level of detail in these maps is unparalleled and makes Google maps look like a tinpot attempt. There are plenty of different maps, ranging from the business use with details including every fixed feature of Great Britain larger than a few metres, to the OS Explorer purposely created for walks and cyclists in mind. Whichever map you’re looking at, the detail is always intricate, bordering on the absurdly small. 


With the word Ordnance in the name, it’s probably not a great surprise that the Ordnance Survey maps have military origins. And this being Britain, with its near-constant internal bickering between the home nations, it’s also not a great surprise that the most comprehensive attempt to map the country came about by the desire to subjugate some of its citizens.   

The Jacobite Rebellion that erupted in 1745 began in the Scottish Highlands and saw Charles Edward Stuart attempt to regain the British throne, in the name of his father, whose father had been king until he was deposed in 1688. Stuart, with the aid of the Scots, marched south, taking Edinburgh and entering England itself in November. The idea was that a French force would land simultaneously in southern England as Stuart joined forces with those in England loyal to his cause, leading to the Stuarts being placed upon the throne once again. 

Things didn’t quite work out, with English support much lower than anticipated and eventually disagreements between the Jacobites bringing an end to the rebellion. The English crown breathed a little easier, but one factor had certainly been emphasised, the complete lack of suitable maps of the Scottish Highlands. As the English began hunting for those responsible for the rebellion, it was like looking for a needle in a haystack. Creating a map now wouldn’t necessarily help with finding the Jacobite rebels, but it might help with pacifying the clans to the north that had been a constant thorn in the side. 

In response, King George II ordered the most detailed map of the region ever compiled and placed Lieutenant-Colonel David Watson in charge. But it was 21-year old William Roy who was given the task of actually making the map and consequently trudging through the undeniably beautiful, yet ruggedly harsh landscape of the Scottish Highlands.  It took Roy 8 years to complete what came to be known as the ‘Great Map’. 

An Anglo-Gallic Dispute

Nothing quite like the Great Map had ever been produced and Roy was keen to widen its scope to include the entire country, but this proposal was turned down in 1763 on the grounds of its exorbitant predicated cost. He kept up the requests but was continuously denied until a debate between Britain and France required his services. 

In 1783, French cartographer and astronomer Cassini de Thury made the bold claim that the latitude and longitude measurements made from the Greenwich Observatory were incorrect. No doubt this irked many in Britain, especially considering it came from a Frenchman, but a decision was taken to combine data taken from both the Greenwich and Paris observatories that might finally settle the matter. 

This involved the construction of the largest ever theodolite – imagine those small machines that you sometimes see engineers peering through but on a much larger scale – and a system referred to as a Triangulation. 

Triangulation is essentially the basis of accurate map-making and involves precise measurements between certain points which comes out looking like a vast series of triangles. Then using good old trigonometry from school, it is possible to calculate distances and angles. This was done on a fairly small scale to settle the debate, mostly in the southeast of England at points that could be then linked up with other markers in France. 

Interestingly, there is absolutely no mention in history as to who was right regarding this particular debate and there has been some suggestion that both sides were wrong – which would probably explain the gap in history. Either way, it was a huge step forward for map-making in Britain and would lead to the first high-precision triangulation survey of the whole of Great Britain. It was on 21st June 1791, that an organisation was formed that would oversee this vast endeavour and that would become iconic in Britain – The Ordnance Survey – then known as the Board of Ordnance. 

The Principal Triangulation of Britain

Considering that William Roy had been advocating for such a project for most of his life, it is a little sad that it got going just a year after his death. 

If the work done to settle the French/British debate had been fairly quick and easy (just the six years) what came next was anything but. Between 1791 and 1853 the mammoth operation known as the Principal Triangulation of Britain set out to precisely measure distances between 300 major landmarks around Britain, which created the first full triangulation of the entire nation. 

Some of the earliest parts done were around the coastline and again it was because of the French. But this time it had nothing to do with cartographer squabbles, but rather the increasing threat of Napoleon invading Britain. With highly accurate maps of the coastline, military leaders believed they would have a better chance of repelling any would-be invaders and the Ordnance Survey was directed to concentrate their early efforts on England’s southern and eastern coasts. 

In 1801, the first detailed Ordnance Survey map using this triangulation was published of the English county Kent and was soon followed by another, Essex. But these early maps were very different to the colourful, reader-friendly versions that we see today. These early maps were all about military use and focused on communication lines and terrain that could be utilized. Probably not so good to find pleasurable walks in and around Barton on the Beans or nearby Newtown Unthank – again, both real places.    

We don’t think too much of it now, but in the early years, place names proved to be quite the issue, for the simple reason that locals frequently argued over names or spelling. Eventually, a Name Book was created where variations of different names could be logged before a final decision could be made. 

These early maps were engraved in reverse on copper plates which were used for printing, with the finished article available for sale for the princely sum of three guineas – the equivalent to around £3.15 today, which sounds cheap, but was actually between one and three weeks wages for the average British person.   

Irish Maps

As work continued slowly on the Ordnance Survey maps in Britain, a group was dispatched across the Irish Sea to begin the first major mapping of Ireland. And no this had very little to do with either the glories of map mapping or military purposes, but because of taxation. 

And if you thought the English cartographers had problems with English places names, then Ireland was an entirely different matter. Considering the English were considered as little more than invaders by the native Irish population, it’s not surprising that there was a high level of suspicion around the map making going on in Ireland around this time, excellently portrayed in Brian Friel’s play Translations which was released in 1980. Many of the anglicised place names found in Ireland date this time, though some have been reverted.  

Early maps of Ireland began appearing in the 1830s, with the final survey completed in 1846. In a strange twist, it was finished shortly before the Irish famine erupted, a catastrophe that would claim roughly a million lives. The Irish Ordnance Survey maps, therefore, became an indispensable tool for studying the area before the famine that decimated much of the country. 

New Era

The colossal triangulation of Britain was concluded in 1853, after a 62-year project. As the threat of war faded and Britain established itself as the colonial overlord of the world, the Victorians set about building vast amounts of railway around Britain, which invariably led to higher interest in maps that could help you once you got off the train. 

One point of contention had always been over the scale of the maps and this was settled around this time, with six inches to the mile (15.2 cm to 1.6 km) for mountain and moorland, 25 inches to the mile (63 cm to 1.6 km) for rural areas, right up to ten and a half feet to the mile (3.2 metres to 1.6 km) for built-up areas. The most detailed map of London ever created was mapped out between 1862 and 1872, and took a huge 326 sheet. To give you a good idea of how quickly London grew around this time, a second edition released in 1895, included 759 sheets.  

And things were changing for the Ordnance Survey too. A fire that had raged through the Tower of London 1841, not only nearly consumed the Crown Jewels but the Ordnance Survey offices – and their precious maps – too. The group moved to a more spacious dwelling in Southampton where they have remained ever since. 

Technological progress saw great changes with both how the maps were made and their physical appearance. Zincography, using zinc sheets, eventually replaced lithography (using stone) as the principal method of printing, with copperplate engravings still used for the one inch (2.5 cm) maps. In 1855, photography began being used in the process and to be a relatively cheap and quick way of enlarging or reducing maps, a process that developed into photozincography.  

In 1887, the Ordnance Survey began releasing colour maps and these became hugely popular as part of the Ordnance Survey Great Britain County Series, which had started all the way back in the 1840s, both to give more detailed coverage of each British county than ever before, but also as a way of establishing parish and land parcels. 

Right up until around 1940, the Ordnance Survey was producing a shadow map system that was restricted from general public viewing. Just like the military maps of old, these maps included details that could be used for the War Office and included landmarks such as dockyards, naval installations, fortifications and military camps. On the regular maps, these areas were left blank or incomplete, which no doubt would have provided plenty of intrigue and an enticing reason to go there for anybody reading the map. 


If you’ve ever been to a war museum and marvelled at the wonderful complexities involved in the maps used during the First and Second World Wars, well now you know why. During World War I, Ordnance Survey personnel were dispatched to France and Belgium to create the maps used on the battlefield. 

Now, I’m going to stick my neck out and say it was better to be a map maker than a soldier in World War I, but it was probably much closer than you’d think. Working under hellish conditions, Ordnance Survey staff created detailed maps of battlefields as well as many of the major towns and cities in the region. In total, at least 25 million battlefield maps were produced for British troops on the ground, and a colossal 342 million.

The break between the two wars saw a huge surge in hiking interest in Britain and the Ordnance Survey were busier than ever. This also led to the Retriangulation of Britain – yes the long-awaited sequel – that took place between 1935 and 1962. Part of this vast endeavour was the establishment of a network of permanent surveying stations built on high points across Britain. These have come to be known as Trig points or Trig Pillars and today there are still 6,500 of them scattered around the nation. The result of this was the Ordnance Survey National Grid reference system, which divided Britain into a huge grid that was distinct from latitude and longitude – a system that is still widely used today.  

the trig pillar
The Trig Point at the summit of Crompton Moor, in Shaw and Crompton, Greater Manchester, England.By Jza84, is licensed under CC-BY-SA

During World War II, Ordnance Survey staff were again pressed into action to create maps of Italy, France, Germany, Holland and Belgium that could be used by troops in Europe. A reported 120 million Ordnance Survey maps were used during the preparations and execution of the D-Day landings, with a total of 342 million created in total.   

Closer to home, their offices were bombed – probably not on purpose as the Luftwaffe were almost certainly going for the Southampton docks and not the non-descript map-making building – and staff were scattered across several buildings as they kept up their end of the war effort.  

Into the Modern World

In 1971, digital mapping was introduced to the map-making process, with photography and aerial surveillance playing an increasingly vital role. In 1995, with the World Wide Web proving to be a big hit already, the Ordnance Survey launched its website and digitised the last of around 230,000 maps. This made Britain the first country in the world to complete a programme of large-scale electronic mapping. 

The way the maps are put together has changed dramatically in the last 50 years with satellites, GPS and aerial imaging now fundamental to the whole process. The recent OS MasterMap, an intelligent geospatial database that gives the most comprehensive detail of Britain ever, now includes more than 460 million man-made and natural landscape features across the country. And to keep up with the rapid pace of change, the Ordnance Survey makes, on average, around 20,000 changes to their database every single day. 

Nowadays paper maps have become curious relics from the past with apps able to summon data from any distant corner of the country in seconds. A lot has changed over 230 years, but the Ordnance Survey continues to do what it always has. Helping us find our way between Nether Wallop and Butt’s Green, while handily keeping tabs on whether the pub in Broughton along the way is still open for business. 

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