Note : This post was first published in 2013. It has been updated.
If you think back just a few years, before the advent of cheap GPS and SatNav devices, we used to find our way about the country using maps. Remember them, large sheets of folded paper accurately showing where everywhere was and enabling you to measure the distance from one place to another and work out routes to get from A to B. What follows is a story of a remarkable man and the origin of modern-day maps in the Great Britain.
A couple of months ago I read a snippet in our local paper about Major-General William Roy who came from Carluke in Lanarkshire and his connection with Hampton, just a few miles from our home in Richmond. For anyone with an interest in old maps of Scotland, Roy is a major figure. As a young man, in the middle of the 18th century, he was employed by the British Army to help with military planning and to produce maps of the road system of Scotland immediately after the Bonnie Prince Charlie led 1745 Jacobite rebellion. It was to start a lifelong career in cartography that would lead to the foundation of the Ordnance Survey and the accurate mapping of the whole of the Great Britain.
In 1780, the exact distance between the observatories at Greenwich and in Paris was unknown. This led to difficulties in correlating some of the astronomical data gathered by these two great institutions. In those days the only accurate way of measuring distances was to painstakingly lie rods of known length end to end between point A and point B. This had been done over some very large distances on land but the English Channel threw up a serious and seemingly insurmountable challenge.
The art of triangulation was understood but not well-developed in England. Triangulation requires the setting up of a baseline whose length can be very accurately measured then from each end measuring the angle to a distant point. Simple trigonometry then allows the calculation of the distance from each end of the baseline to the chosen distant point. It’s a slow, laborious task but, over time, the relative distances between all points can be calculated and maps drawn. And, of course, this technique can be used across water as well as land providing there is a line of sight from one side to the other. For the process to work it is crucial that the baseline is a few miles long and is over level ground so that its length can be accurately measured.
William Roy was the obvious candidate for the job and his first crucial task was to identify the best place for the baseline. To the west of London there was a vast area of heathland, Hounslow Heath, that was virtually flat from one side to the other. Roy decided he wanted a baseline of about 5 miles in length and he set about selecting the line across the heath, marking the ends and painstakingly measuring its exact length initially with wooden rods. These rods proved to have too many inaccuracies due to the effects of water and temperature. They were replaced with glass rods and accuracy improved dramatically. His measurements proved so accurate that, many years later, when more sophisticated measuring was possible, he was found to be about two inches out. Not bad. Even with modern day GPS his measurements have been shown to be accurate to within less than thirty feet. Quite an achievement.
Being the devout cartophile that I am, it was essential to go and look at Roy’s baseline and soak up the atmosphere. A little research soon identified the exact location of the end points. A look at the 1:25,000 Ordnance Survey map of London South – most appropriate given the nature of the expedition ahead – highlighted the fact that the north western section of the base line goes right across modern-day Heathrow Airport and other parts have been built over with housing, warehouses and factories. It clearly wasn’t practical to “walk the line” as Johnnie Cash memorably sang. However, the modern passion for establishing footpaths with a recreational purpose, led me to look at a section of the London Loop that passed near both ends of the baseline. This could provide a good walking route albeit a slightly circuitous one adding a couple of miles to the length of the baseline.
So on a cloudy, warm and humid Thursday afternoon with rain threatening, I set off on an R70 bus from Richmond Bus Station to the appropriately named Roy Grove, the site of the south west end of the baseline. The bus was brand new and on its first day in service but the driver of the bus had to apologise for the faulty heating system that was blasting out hot air. It was a relief to arrive in Hampton and alight at the corner of Roy Grove. The street is a quiet cul-de-sac of neat, post-war council houses with the tell-tale individual front doors of houses that were sold off during the Thatcher era.
The exact end-point was easy to find. Two cannons from Greenwich, were dug into the ground to mark the end points with the barrels pointing vertically and with about three feet above the ground. In 1926, to commemorate the 200th anniversary of the birth of Roy, a plaque was erected on the site. And the Twickenham Council at the time that the houses were built in 1947, had respected the historical value of the baseline and had left a good plot of grass around the cannon.
The view along the baseline illustrates Roy’s choice of terrain precisely. It is completely flat as far as the eye can see. Although much of Hounslow Heath is now built upon so you can’t see from one end of the line to the other, the lack of any raised ground is pretty apparent.
One of the suggested routes between the two endpoints was to take the 285 bus which has a stop two minutes away from Roy Grove and another stop even closer to the other endpoint on the Northern Perimeter of Heathrow. It follows a route almost parallel to the baseline – apart from a diversion to avoid crossing both the northern and southern Heathrow runways. As mentioned earlier my sights were set on walking between the two endpoints so I set off up the Uxbridge Road to join the London Loop about 3/4 mile to the north.
At this point The Loop leaves the road behind and traverses the edge of the Twickenham Golf Course, through a housing estate, across the Great Chertsey Road to the banks of the River Crane. Technically The Loop follows the east bank of the river but I have walked and cycled that path on numerous occasions so today, in the spirit of adventure and using my OS map courtesy of Roy’s pioneering work, I joined the path on the west bank. The path is well made with excellent drainage and about 8 feet wide, in sharp contrast to the eastern path which changes surface every few yards and has muddy sections even on the driest of days.
The path had a few picturesque sections alongside the river but it didn’t pass the one major industrial artifact that is on the other bank. This structure is an old gunpowder mill and, thanks to some recent restoration, is well worth a visit. But not today. The river then disappears under the Hanworth Road and here the paths stop. The next stretch is built up with houses, factories and warehouses and, if you tried to work a way through them, you would come to the impenetrable barrier formed by the Hounslow branch of the Waterloo to Staines railway line. So The London Loop follows the road towards Hounslow and then, having crossed the railway by a road bridge, takes a left turn that leads via a small housing scheme onto Hounslow Heath.
I’ve never been on the Heath and wasn’t at all sure what to expect. The first reaction was how remote it soon started to feel. An occasional person, usually a dog walker or a bramble picker, came into view but as quickly disappeared again. Hounslow Heath in Roy’s days had a reputation as the home of highwaymen. Although the Heath is only a fraction of the size it was in the 18th century you could still imagine the modern-day equivalent, muggers, could flourish in this urban wilderness. And my unease was not helped when I came across a rope hanging from a tree – was rough justice still practiced here???
Soon after the rope, civilisation intruded in the form of Hounslow Heath Golf Course. The path crossed a fairway near to the 7th tee but there was no sign of golfers today. Up to this point the route had mostly been across open land with scrub and small copses of trees. Now it came back to my old friend the River Crane, entered woodland and followed the river for the next 3/4 mile till it emerged suddenly in a BP petrol station forecourt beside a busy arterial road. What a contrast, from rural idyll to urban nightmare in ten paces.
I’d noticed a number of small weirs in the river, the tell-tale signs of old mills. An information board indicated that this bit of woodland was called Brazil Mill Wood after the biggest mill on the Crane near this point. The name comes from the Brazil nuts that it ground to make dyes for the paper and calico industries that also flourished on the Crane in the 18th and 19th centuries. Another major product of the mills in the area was, as mentioned earlier, gunpowder, which utilised the local willows and alders to make the essential ingredient of charcoal. Clearly this had been a thriving community back in the days of the Industrial Revolution.
When you are walking in woodland the view of the sky is basically restricted to what is immediately overhead. On entering the petrol station forecourt it became apparent that some very black clouds had been building up to the west and rain was but minutes away. Discretion being the better part of valour and a 285 bus stop being less than 1/2 mile away, it was time to abandon The London Loop and make a dash for shelter. I didn’t feel too bad about this change of plan. As mentioned earlier the 285 route follows the Roy’s baseline as closely as is possible.
The heavens opened as I reached the bus stop so I joined a small group of people huddled in the bus shelter. The bus arrived within a few minutes. Heathrow was now within sight and the route passed by many of the warehouses and offices of the businesses that service the airport. And then, with a link back to the past of Hounslow Heath, we passed Dick Turpin Way. History records that Turpin probably only carried out one highway robbery on Hounslow Heath preferring to ply his trade in East and North London. In fact, contrary to popular folklore, Turpin was no gentleman thief, he was a really seedy villain and murderer. He only took up highway robbery in the latter years of his short life. I wonder if the Council was in full possession of the facts when naming this short road after him.
Back to the expedition. After Hatton Cross, the bus and tube hub serving the south side of the airport, the bus route takes the inevitable diversion from Roy’s baseline to avoid crossing the two main runways and driving through the gigantic aircraft hangers. It finishes by going along the Bath Road on the north side of the airport. It was time to get off, just before the bus headed through the tunnel to the central area of the airport. And it was at this point that I realised that I had forgotten to print out some vital instructions; the directions to the end of the baseline. Calamity. All I remembered was that it was in the Business Parking area on the North side of the airport above the entrance to the tunnel that takes traffic to Terminals 1, 2 and 3.
Undaunted, I started to walk round the parking lots trying to avoid being picked up as a car thief or even as a trespasser! At one point a courtesy bus stopped and the driver asked if I was going to Terminal 1. No, I said, I’m looking for a cannon. He looked a bit confused to say the least and suggested I try calling the authorities on the help telephones that were scattered about. I’d visions of blue flashing lights and a lot more explaining to do so took the cowards way out and walked smartly to the nearest exit. So near and yet so far.
And then luck kicked back in. On the way in I’d passed, without noticing, a concrete tablet beside a roundabout at the top of the tunnel slip road. On the way back it caught my eye and help was at hand. The tablet bore an inscription as follows :-
“109 yards to the south of this tablet is THE NORTH WEST TERMINAL OF THE FIRST BASELINE OF THE TRIANGULATION OF GREAT BRITAIN. The base was measured in 1784 by MAJOR-GENERAL WILLIAM ROY FRS the Father of the Ordnance Survey”
Directions at last. And right enough, after dodging traffic using the roundabout and the slip road – there’s no provision for pedestrians here – at the junction of Nene Road with the Northern Perimeter Road and nestling in a corner of the Business Parking fence, was the elusive cannon barrel pointing skywards exactly as in Hampton. I’d made it.
The cannon is actually outside of the car parks but only just. The security fence makes a neat diversion leaving the marker visible and accessible to all. Having said that, how many of the tens of thousands of people every day who pass within feet realise that they are passing a monument to a major event in the development of the mapping of the Great Britain.
It may sound a bit nerdy to talk in these terms but just think where we would be now if no one had worked out how to measure distances accurately and to produce the world class maps of the Ordnance Survey. So next time you set your SatNav, remember Major-General William Roy FRS, the pioneer of mapping in the UK.