OSNI 

Ordnance Survey of Northern Ireland covers Northern Ireland 

View OSNI mapping on-line 

OSI 

Ordnance Survey of Ireland covers the Irish Republic 

View OSI mapping on-line 
 

Short Histories by Dr. Richard Oliver

• Ireland within the United Kingdom : 1824-1922
• The Free State and the Irish Republic : 1922 to date
• Northern Ireland : 1922 to date

Other Related 

See OSI website for more information about Ordnance Survey Ireland 

See OSNI website for more information about Ordnance Survey of Northern Ireland (Now part of Land and Property Services)