The long road to mapping Great Britain.

This month sees the release of the latest updated Ordnance Survey maps of Great Britain, which have been in existence for 225 years. But their genesis was even earlier.

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The officially recognised date as the birth of Ordnance Survey, Britain’s mapping agency, is June 1791 but it has its roots in military strategy; the mapping of the Scottish Highlands following the Jacobite rebellion of 1745.

William Roy, a 21 year-old engineer, was tasked by the Board of Ordnance (the defence ministry of the day), with the initial small-scale military survey of Scotland, the first government-made survey of a substantial tract of the British Isles.

Beginning in 1747, it took eight years to complete what was known as the Great Map at a scale of 1:36 000 (1.75 inches to a mile). Roads, hills, rivers, types of land cover and settlements were recorded. Roy himself described it as more of a “magnificent military sketch than a very accurate map of the country.”

The surveying parties relied on simple surveying compasses to measure the angles, and chains up to 50 feet long to measure distance between important features. Much of the rest was sketched in by eye. Nevertheless, the map was a powerful tool as part of a broader strategy to open up access to the Highlands.

In 1763, 1766 and 1783 Roy made proposals for a complete official survey of Britain but all these proposals failed because the cost was considered excessive.

The real start of work which can be recognised as ‘Ordnance Survey’ came in 1783-4, when the Royal Societies of London and Paris worked out the relative positions of the astronomical observatories in their two cities by connecting them by a system of triangulation. Until the recent advent of GPS, triangulation was the universal means of providing a skeleton for controlling survey operations, and was the only feasible way of measuring distance across water and other obstacles where ground measurement by chains or tapes was impractical.

As the leading geodesist of the day the English part of the operation came under the Roy’s direction. His lifelong ambition was to produce a superior map of Britain, unparalleled in its accuracy and by the time of his death in 1790, with the London-Paris triangulation completed, he was thinking of using its extension as a basis for further survey work in Britain.

The Master-General of the Ordnance, who was sympathetic to Roy’s ideas, authorised the expenditure of £373.14s of national funds to purchase a newly-designed theodolite on 21st June 1791 and this date has since been taken as the official ‘foundation date’ of the Ordnance Survey.

By 1823 it had covered much of Britain.

The latest OS maps of Britain are now available across many platforms including the TX4 GPS and will soon be available for 7” tablets. You can even step back in time with historical OS maps from the 1800s, 1900s, 1920s and 1940s and see how OS maps have changed over time. All are available now from Memory-Map.

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