The Mapping of
Many navigators, (as well as any other folk that may be interested in maps,) may like to know the story of how our Country came to be surveyed and mapped, ending with the Ordnance Survey Maps without which, for instance, the sport of rallying would be a rather difficult task for the organisers! Let’s start with a little bit of history…
Part 1 “THE HISTORY OF BRITISH MAPPING”
he first set of maps of
This scale continued to be the standard scale of British mapping until the Ordnance Survey announced that it was changing to metric scales in 1965. The first OS 1:50,000 metric map was produced in 1974.
The Society’s prizes were taken up with enthusiasm and a large number of individual county maps were produced over the next thirty years; but it soon became clear that these maps were unsuitable for military purposes which was the Government’s only concern. The idea of a full scientific national survey must be credited to William Roy (1726-1790) who was a civilian draughtsman with the army’s Board of Ordnance at its Edinburgh Office.
Following the Jacobite uprising which culminated in the battle of Culloden in 1746, George II realised that accurate maps of
In 1763, the war now over, Roy realised how vulnerable Britain was to invasion and proposed a full national survey for defence purposes, but the Government declined on the grounds of cost.
But Roy also realised that even triangulation required a precisely measured base line a few miles long as a starting point and he chose the flat lands of Hounslow Heath, the site of Heathrow Airport today, as his starting point.
Roy tried and rejected several measuring methods such as rods of wood and iron and eventually settled on the use of glass tubes 20’ long and 1” in diameter which were unaffected by temperature and humidity. This was the first precisely measured base line in
By this time the new King, George III, was anxious to cooperate with the French, who were disputing the exact position (ie latitude) of the Greenwich Observatory whilst promoting their own surveys based on the Paris Observatory. The King agreed to fund a survey of the south east corner of England which could match up to the surveys already completed in northern France by triangulation across the Channel.
Charles Lennox, 3rd Duke of Richmond had been appointed Master General of the Board of Ordnance in 1782. The role of the Board was to deal with the army’s fortifications, small arms and munitions.
The Ordnance Survey was born.
The First OS Maps.
The data collected during the triangulation of the south east coast was expanded by detailed ‘topological’ survey work on the ground and the results were passed on to the mapmakers at the Survey’s headquarters in the Tower of London. In 1801 the first OS map (Number 1) covering the
The surveying continued, first along the south coast because the maps were still essentially for military defence purposes, and then gradually northwards. The process was the same throughout: first the primary triangulation with triangle ‘legs’ about 30 miles long, then the secondary triangulation with approximately 5 mile legs inside the primary triangles, then the detailed topographical survey on the ground prepared a survey at a scale of 6 inches to one mile. All this data was passed to the engravers and printers who produced the one-inch maps.
Copyright was always a contentious issue and there were many infringement cases against commercial mapmakers who merely copied the OS maps. For most of the time the OS maps were sold to the public though few could afford them at the equivalent of £50 per map at current prices.
This first national survey was completed in 1841.
Over the next hundred years the initial survey was revised continually and was extended to include
By the 1930s, however, massive changes to the landscape, especially in urban areas, made it clear that a complete new survey was needed, and a new national primary triangulation was started under the auspices of Captain Martin Hotine in 1935.
The New Survey.
Hotine realised that war was looming again so he pushed the survey ahead quickly. First the triangulation sites were recce’d, often using the same sites as the original triangulation 100 years before. The hilltop sites were cleared of undergrowth and new sites established where the original could not be used. Next the pillars were constructed on the sites – these are the still familiar concrete ‘triangulation pillars’ better known as ‘trig points’ so beloved by Navscat organisers.
The Second World War intervened but the national re-triangulation was completed by 1957. A new base line for the re-triangulation was measured along the
An embarrassing mistake.
Throughout this time, secondary triangulation and on-the-ground surveys followed the main observations. This revealed an interesting mistake made a century earlier. The Greenwich Meridian (0° longitude) had been defined by Bradley’s transit instrument in the Greenwich Observatory up to 1850 and this position had been used by the OS as the definitive 0°. The new Astronomer Royal, Sir George Airy, built a new transit instrument in 1850 that he positioned at
Up to date.
Aerial photography suffered in its early days from lack of sufficiently good equipment, but advances in techniques have ensured that the days of the ground survey were soon to be over. It is interesting to note that the aerial surveys still relied on the trig points to locate precisely the overall positioning controls for the aerial maps. In fact, trig points were repainted in bright white just so that they could be easily seen on the aerial photographs. It didn’t matter that many of the trig points could no longer be seen from adjacent triangulation points so long as they could be spotted from the air!
Measuring methods also advanced from the 1950s. The Swedish Geodimeter issued a pulsed light beam that could be reflected back to the observer and this was tested by the US Army Mapping Service on the Ordnance Survey’s
Since the 1980s Global Positioning Systems (GPS) using satellites have been widely used and since 1990 the two hundred year old triangulation methods have no longer been used for the primary survey. For the future the mapping scientists are looking to intergalactic bodies such as pulsars and quasars to enable distances such as the complete length of