The maps collection held by the National Library of Scotland is one of the finest in the world, and the foundation of the collection are the Ordnance Survey maps first produced in the mid-19th century. These maps, and those that followed, were made possible by a process called triangulation.
Triangulation is a means of determining the location of a fixed point by measuring angles to it from other fixed points. The original triangulation of Great Britain, called Principal Triangulation, was carried out between 1784 and 1853, and provided the foundation for the Ordnance Survey mapping of the country. In 1935 the Director-General of the Ordnance Survey, Major-General Malcolm MacLeod, set out to modernise the country’s triangulation, and in a military style operation, called Retriangulation, running from 1936 to 1962, hundreds of triangulation stations, or ‘trig points’, were carried up hills and mountains in order to make the mapping of the country more accurate. Several thousand secondary points were placed across the country.