Triangulation of Great Britain) 海平面 英國地形測量局目前僅處理大不列顛島及馬恩島的地圖。北愛爾蘭雖然是英國的組成部分,但相關事務由獨立的政府機構北愛爾蘭地形測量局(英语:OrdnanceSurveyofNorthernIreland)專責。 OrdnanceSurvey Annual
Culture NorthernIreland website. OrdnanceSurvey Memoirs ofIreland, Parishes of County Antrim V111, Vol 23, 1831-5,1837-8. The Institute of Irish Studies
Robert Scott. 1928: 14–21. OrdnanceSurvey data City of London Resident Population 2001 – Historical trends (PDF). City of London Corporation. 2005-07-01