OSNI Open Data - Historical Six Inch to One Mile County Series Edition 1 (1829 - 1835) - Armagh

The OSNI Historical Archive service is created from the 6 inch County Series mapping. The maps are georeferenced to the Irish Grid, having been adjusted to transform the original Cassini-Soldner projection to the current Transverse Mercator projection, allowing a reasonable degree of fit. As each county was surveyed separately, there is not a perfect fit between the transformed sheets, resulting in some overlap along the borders between counties. However the discrepancies are minimal and the full data is provided with no overlap. They are derived from original surveying scales of six-inch to one mile. There are four full editions: Edition 1 (1829 – 1835), Edition 2 (1848 – 1862), Edition 3 (1899 - 1908), Edition 4 (1902 - 1957).