Nick Woods celebrates two hundred years of the Ordnance Survey ‘1 inch’ map
Published in September ’11
The first one-inch-to-a-mile Ordnance Survey maps of Dorset were produced, in black and white, on printing presses in the Tower of London in 1811. The equivalent maps of the whole county can now be stored on a memory card the size of a postage stamp, and displayed, in full colour, on a hand-held Global Positioning System (GPS) unit. This remarkable technology can display your location, accurate to within a few yards, thanks to the satellites now orbiting the earth. The Ordnance Survey has a fascinating history and the various maps produced over the last two centuries also vividly illustrate the way the county itself has changed since 1811.
The origins of the Ordnance Survey go back to problems the military faced in dealing with the Jacobite Rebellion in Scotland early in the 18th century. As a result, William Roy, ‘Surveyor-General of coasts and Engineer for making surveys under the Honourable Board of Ordnance’ undertook the ‘The Military Survey of Scotland’ between 1747 and 1755. Eleven years later he lobbied King George III for the making of a ‘General Military Map of England’, but military commitments around the world meant it would be another twenty-five years before such a survey would start in earnest. In fact, the first inch-to-the-mile map of Dorset was not produced by the military at all. In 1759 the Royal Society of Arts had offered a prize of £100 for an accurate survey of any county at this scale. One candidate for the prize, Isaac Taylor’s 1765 map of Dorset, was rejected by the Society as too inaccurate. The accuracy required would involve the use of trigonometry – the calculation of the distances between three points of a triangle by measuring the length of its base and the angles to the apex – on a giant scale across the whole country.
Such an endeavour needed a large open and flat area for the initial baseline. In 1784 William Roy had found such a site on Hounslow Heath, an area large enough and flat enough to later accommodate Heathrow Airport. Roy’s aim was to fix precisely the position of the astronomical observatories at Greenwich and Paris, both important points of reference for seafarers calculating their latitude and longitude. The painstaking measurement of the five mile baseline took seventy-five days and captured the public imagination, with an enthusiastic King George III amongst those visiting the site.
The King was an avid supporter of scientific projects characteristic of the ‘Age of Enlightenment’. His finance, along with that from the Military, led to William Mudge and Isaac Dalby, of the ‘Trigonometrical Survey of the Board of Ordnance’ re-measuring Roy’s baseline in 1791 as the starting point for a survey of the whole country. A high quality theodolite, a telescope mounted on a turntable, was required for the precise measurements of the angles and this was purchased from Jesse Ramsden, renowned for the quality of his instruments, but not always reliable as to delivery times. The King was also one of his customers, and reputedly described Ramsden as the ‘least punctual of any man in England’ when he delivered an instrument at the right time, on the right day but twelve months late.
Fears of a French invasion gave the mapping a renewed impetus, especially along the south coast. Mudge and Dalby extended the triangulation into Dorset in 1794 using Nine Barrow Down on the Purbeck ridge as a key station and creating triangles to Black Down, Bulbarrow, Win Green, Pilsdon Pen and Golden Cap. More detailed mapping of the area was then undertaken by the ‘Interior Survey’ to produce the actual maps.
The Dorset maps were originally published in April 1811, but sales were halted in September of that year due to renewed fears of a French invasion. The ban was lifted in 1816 and the Times advertised the ‘new and accurate maps drawn from actual surveys’. The four Dorset sheets were available for three guineas, roughly equivalent at the time to a Dorset farm labourer’s wages for nine weeks. Today the modern version of such maps retail at £6.99 each and a set covering the county would cost four and a half hours’ pay at the minimum wage. Two weeks of such wages could buy these maps on a memory card, plus the GPS unit to view them on as well as unlimited use of the satellite location system (currently maintained by the US Government at an annual cost of around $400 million).
Despite the success of the maps not everyone was happy. In 1862 the Times carried a letter from a disgruntled customer from Weymouth complaining that the one inch map had not been updated to include the ‘extensive additions to Weymouth and neighbourhood’ or many of the recently constructed railways. Rapid urbanisation meant maps were soon out of date and more detailed maps were also in demand, culminating in the publication of Town Plans at a scale of over ten feet to the mile. These incredibly detailed maps, published between 1855 and 1895, covered towns with a population greater than 4000, including Bournemouth, Bridport, Christchurch, Dorchester, Poole, Sherborne and Weymouth.
Life was not always straightforward for the surveyors either as they traversed the country. As early as 1818 one surveyor complained about the ‘swarms of idle holiday visitors’ making progress difficult and in 1848 Punch published a cartoon showing a frightened woman convinced the surveyor’s tripod bore a blunderbuss rather than a surveying instrument. The surveyors still needed to reach the best viewpoints and they carted heavy equipment to sites as varied as the summit of Mount Snowdon and the very to the top of the dome of St. Paul’s Cathedral. The demands on the Ordnance Survey meant that publication of the one-inch maps would not be completed until 1887; seventy-six years after the Dorset sheets were first published. Triangulation would remain a key technique for over a century and later surveys left a legacy of concrete ‘trig points’ scattered across the landscape. These are largely obsolete now as the Ordnance Survey uses its two aircraft, satellites and GPS to supplement work on the ground.
Early Ordnance Survey maps are now important historical documents. Editions covering the last century or so may still be picked up in second-hand bookshops and Cassini publishes old and new versions of maps side by side.
Many old maps are also available on the internet, including the results of the 1930s Land Utilization Survey organised by the eminent geographer Dudley Stamp. Unlike even the most detailed Ordnance Survey maps, this survey, undertaken largely by school children and students, distinguished between arable land and meadow. The sheets had a practical application in the Second World War when many were used by the Agricultural Emergency Committees to help improve food production.
Two hundred years after the publication of Dorset’s first Ordnance Survey map, such documents are still of immense practical value and historical interest. If an early surveyor could return he would probably be taken aback by the growth of our towns but amazed, and highly appreciative, of the modern technology that we now use to make, distribute and enjoy our maps.
1. British Library Board shelf mark OSD66 and the modern map on a GPS unit (courtesy of Satmap Systems Ltd)
2. The Royal Society
3. City of London/London Metropolitan Archives
4. courtesy of Cassini Publishing Ltd, www.cassinimaps.com
5. courtesy of Vision of Britain website and the Environment Agency/DEFRA