From French Invasions to Google Maps: The History of Mapping Britain
We take maps for granted. Open your phone, type in a postcode and within seconds you can see exactly where you are, where you're going and, importantly, how long it will take you to get there.
But Britain wasn't always neatly covered in detailed maps.
In fact, the story of how Britain was mapped involves French invasion fears, giant scientific instruments, soldiers clambering up mountains, concrete pillars, hot air balloons and an astonishing amount of measuring things.
So, how did we get from “I think the village is somewhere over there” to Google Maps?
Britain before accurate maps
People had been making maps of Britain for centuries before the Ordnance Survey existed. Early maps were useful, but they could be surprisingly inaccurate. Coastlines, roads, rivers and settlements might be shown, but there was no single, highly accurate survey of the entire country.
Things became rather more serious after the Jacobite Rising of 1745. The government realised that knowing exactly what the Scottish landscape looked like was rather useful if you were trying to move an army around it.
A young military engineer called William Roy was tasked with surveying Scotland. Starting in 1747, his team spent eight years measuring the landscape, recording roads, rivers, hills, settlements and terrain. They used chains to measure distances and surveying compasses to measure angles. (Ordnance Survey)
Roy became convinced that Britain needed something much bigger: a proper, accurate national map.
Then the French got involved...
Fast forward to the 1790s and Britain was getting increasingly nervous about revolutionary France.
The government was worried about a possible French invasion, so mapping suddenly became a matter of national defence. The vulnerable southern coast was a particular concern.
This was where the Board of Ordnance came in — essentially the government department responsible for military equipment and fortifications.
On 21 June 1791, the Board of Ordnance purchased an enormous three-foot-long theodolite made by instrument maker Jesse Ramsden. This event is regarded as the foundation of the Ordnance Survey. (Ordnance Survey)
And yes, the instrument was huge.
What is a theodolite?
A theodolite is a surveying instrument used to measure angles.
The clever bit was triangulation. Surveyors would measure one known distance and then create a network of triangles across the landscape. By measuring the angles, they could calculate distances without having to physically measure every single one.
Think of it as the world's most complicated game of join the dots.
The surveyors began building a giant network of these triangles across Britain. Some of the famous concrete trig pillars that later appeared on Britain's hills and mountains were part of this enormous surveying tradition.
Britain's first Ordnance Survey map
The first official Ordnance Survey map was published in 1801 and covered Kent.
Why Kent?
Because if Napoleon's armies were going to invade Britain from France, Kent was rather inconveniently located right in the firing line.
The map took three years to complete and was originally produced at a scale of two inches to one mile before being reduced for printing. It contained detailed information about roads, terrain and the landscape — information that could be extremely useful to the military. (Ordnance Survey)
It was also very expensive. A county survey cost three guineas — around £3 3s — which could represent one to three weeks' wages for an average worker.
So your average Georgian family probably wasn't popping out to buy one as a birthday present.
Mapping Britain was a VERY long job
The original plan was ambitious. It was thought that the whole country might take around 50 years to map.
It actually took considerably longer.
The first complete series wasn't published until 1870. (Ordnance Survey)
And remember, this was all being done without cars, aeroplanes, satellites, GPS or Google Street View.
Surveyors physically travelled across the landscape, carrying equipment and painstakingly recording what they could see.
Maps become part of everyday life
Over the 19th and 20th centuries, maps gradually stopped being something primarily useful to the military.
They became essential for engineers, railway companies, walkers, cyclists, motorists, explorers and ordinary people.
Photography was introduced into the map-making process in the 1850s, helping surveyors reproduce and update maps more efficiently. Later came aerial photography, computers and eventually digital mapping. (Ordnance Survey)
During the First World War, Ordnance Survey returned to its military roots and produced millions of maps. During the Second World War, the figure became enormous: approximately 342 million maps were produced for the war effort. (Ordnance Survey)
Maps are history you can hang on your wall
One of the wonderful things about old maps is that they don't just tell you where somewhere is. They tell you what somewhere used to be.
Look closely at an old London map and you'll find streets that have disappeared, railway lines that have changed, fields that became housing estates and neighbourhoods that look completely different.
That's part of the inspiration behind the Planet Patrol map collection, where historic and contemporary London locations are turned into hand screen-printed artwork.
You can explore prints of places including Shoreditch, Columbia Road and historic London — turning the geography of familiar places into something you can actually live with, rather than something folded up in the glove compartment.
The map is never really finished
Perhaps the strangest thing about maps is that they're never truly finished.
Cities grow. Roads move. Railway lines disappear. New buildings appear. Old buildings are demolished.
Even today, mapping organisations are constantly updating geographical information. Ordnance Survey describes itself as Britain's national mapping service and now maintains hundreds of millions of geographical features in its national database. (Ordnance Survey)
So the next time you look at a map, remember: you're looking at a snapshot of history.
And somewhere underneath that familiar street, road or neighbourhood could be an old field, a vanished railway, a medieval path — or possibly a surveyor from 1791 standing on a hill with an enormous telescope, desperately trying to work out where the French might land.
Not bad for something that started with people measuring triangles.