The Ordnance Survey Office, established in 1824, was created to carry out a military survey of the entire island of Ireland to update land valuations for land taxation purposes. The original survey at a scale of 6 inches to 1 mile was completed under the direction of Major General Colby. Ireland thus became the first country in the world to be entirely mapped at such a detailed scale. When the survey of the whole country was completed in 1846, it was a world first.
Particularly relevant for genealogy or those with an interest in the history of a place, these "6-inch" maps include every tiny house or cabin that was likely occupied before the Famine. The good news is that the OSi has captured this and later mapping data in a digitised format, and they are free to inspect online.
VIEW MAPS Click here to explore the entire archive of historic maps (for the earliest maps check out the 6-inch colour maps).
ALSO READ: Your ROSCOMMON parish just before the famine