The United Kingdom (UK), officially the United Kingdom of Great Britain and Northern Ireland, is a country in western Europe. Lying off the north-western coast of the European mainland, the United Kingdom includes the island of Great Britain (itself made up of England, Scotland and Wales), the north-eastern part of the island of Ireland and many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state — the Republic of Ireland. Apart from this land border, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to its east, the English Channel to its south and the Celtic Sea to its south-south-west, giving it the 12th-longest coastline in the world. The Irish Sea lies between Great Britain and Ireland. The capital and most populous city is London, located in the south-east of the island of Great Britain.