Mapping city, town and country since 1824: the Ordnance Survey in Ireland - RIA Library/IHTA Lunchtime Lectures See accompanying powerpoint presentation. Day describes the work of the OS and in particular, of the Hill Drawing and Topographical Departments. She refers to the intellectual breadth of Colby and Larcom, the two key drivers of the Survey in Ireland and their connections with the main intellectual societies in Britain and Europe. The role played by the Irish Survey vis-à-vis the Trigonometrical Survey of India, led by George Everest, is discussed. The military training included drawing skills and some of the major exponents of artistic endeavour in the military wing of the OS are presented. Finally, the 1,600 drawings contained in the OS Memoirs are discussed in terms of their content, level of skill and their role in the Survey.