The Republic of Ireland–United Kingdom border, sometimes referred to as the Irish border, runs for 499 kilometers Ordnance Survey of Northern Ireland, 1999 [https://www.qub.ac.uk/research-centres/CentreforInternationalBordersResearch/Publications/WorkingPapers/MappingFrontiersworkingpapers/Filetoupload,175395,en.pdf MFPP Working Paper No.