Complex sentence: Ordnance Survey Ireland (OSI;) is the national mapping agency of Ireland and, together with Ordnance Survey of Northern Ireland (OSNI), succeeded, after 1922, the Irish operations of the British Ordnance Survey.
Split into simpler sentences: Ordnance Survey Ireland (OSI;) is the national mapping agency of Ireland. It and the Ordnance Survey of Northern Ireland (OSNI) are the ultimate successors to the Irish operations of the British Ordnance Survey.