Local legacy of world first mapping project marked at conference

The Mapping Monuments project, funded by The National Lottery Heritage Fund marked the end of the project with a conference in Ballykelly on Friday 17 November.

In the late 1820s and 1830s, the countryside around Lough Foyle was busy with surveyors occupied with measuring and mapping landscapes for the Ordnance Survey. It was the world’s first large scale mapping of an entire country, and to complete the work surveyors used chains, theodolites and limelight to calculate distances and heights across the landscape.Since November 2021, over 20 volunteers have been carrying out fieldwork and local research to find traces of the Ordnance Survey in the Lough Foyle landscape. This included creating an inventory of local benchmarks on buildings, walls and bridges, archival research and for the first-time geophysical survey of one of the surveyors’ encampment sites at Bellarena Estate. The results of this research has been added to the project website go.qub.ac.uk/MappingMonuments.Many farmers or building owners unknowingly had traces of the Ordnance Survey chiselled into their buildings or walls in the form of benchmarks, sometimes referred to as ‘crow’s feet’. Before the digital age, these were an essential part of the surveying process necessary for determining heights.Professor Keith Lilley from Queen’s University Belfast who led the Mapping Monuments Project said: “2024 is a significant year as it marks the bicentenary of the start of the Ordnance Survey’s field-operations, beginning on the north coast.

“A crucial part of this mapping was the careful and accurate measurement of the Lough Foyle baseline, stretching for eight miles from Ballykelly to Magilligan. Although this line through the landscape is invisible, its presence is marked by the three circular ‘towers’ constructed by the surveyors at Ballykelly, Minearny and Ballymullholland. This surveying heritage is of global significance and our Mapping Monuments project has helped put it more firmly on the map.”

The Mapping Monuments conference was opened by broadcaster Joe Mahon who reflected on how one of the Ordnance Survey surveyors of the 1830s, John O’Donovan had influenced his career.

Grace McAlister, historic environment project officer with Causeway Coast and Glens Heritage Trust, said: “It’s fantastic to bring a conference like this to Ballykelly, and to have so much interest from the local community.“While the Ordnance Survey of Ireland can be difficult heritage for many due to its colonial associations, it was an internationally significant mathematical feat grounded in the local area.

“In addition, the Ordnance Survey memoirs that were produced alongside the map-making captured invaluable social and cultural information from the time.”

If you have any stories relating to Ordnance Survey heritage or know of any unusual benchmarks, please contact Grace McAlister [email protected]/07951371570.