1st January 1825
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The Ordnance Survey of Ireland (1829 - 1842) was the first large-scale survey of an entire country in the world. Acclaimed for their accuracy, these maps are regarded as among the finest ever produced. For the family historian, they can identify the lay of the land in the decades preceding the famine and, most importantly, the homes that had been vacated by the time of Griffith's Primary Valuation.

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.

Major Thomas Frederick Colby (Director of the First OS)

A picture of Major Thomas Frederick Colby who was responsible of the Ordnance Survey of Ireland.

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 mapped data in a digitised format, and they are free to inspect online. 

The first edition of these maps (the 6-ich colour maps) and additional mapping data can be explored free online via OSi (Ordnance Survey Ireland) and OSNI (Ordnance Survey of Northern Ireland).

READ MORE A short history of the Ordnance Survey on Ireland    ALSO  Finding & Navigating Old Irish Maps

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  • How does this survey relate to the Griffiths Survey of Ireland, 1864. Did Griffiths use the Ordinance maps.


    Saturday 2nd November 2019 07:12PM
  • Yes, they did. 

    For more about the various survey maps, see Finding & Navigating Old Irish Maps.


    Friday 18th December 2020 11:30AM
  • IrelandXO_DM

    Sunday 15th May 2022 04:13AM
  • The maps don't seem to cover NI even though it was a whole of Ireland mapping/survey exercise.


    Sunday 15th May 2022 10:27AM
  • Is there a way of finding the name of surveyors who did the surveying? I recall being told by Canon Metcalfe in Kilmore rectory, Co Roscommon that Patrick Marlow, the maternal grandfather of my maternal grandmother was a surveyor. I think the dates look about right for that first ordnance surveying project. I Canon Metcalf looking through a very thick book that held relevant information. I was a young child at the time visiting my aunt and ‘rambling’ on my own into the houses around the village. Such freedom!


    Wednesday 26th April 2023 08:35PM
  • How does one sign in to use the OSI viewer?  It seems to require access through an organization with no way of creating an account.


    Friday 25th August 2023 03:06AM
  • You can view the maps by clicking the link below


    IrelandXO Moderator DC

    Monday 28th August 2023 04:14PM

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