This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The United Kingdom this atlas records today is the product of three separate acts of union, each changing what the word Britain actually meant. The first, in 1707, joined the once-independent Kingdoms of England and Scotland, which had shared a monarch since 1603 but kept separate parliaments until the Acts of Union dissolved both and created a single Parliament of Great Britain at Westminster. The second, in 1801, joined that Kingdom of Great Britain with the Kingdom of Ireland, forming the United Kingdom of Great Britain and Ireland, a state that governed the whole of the British Isles as a single political unit for over a century. The third came in 1922, not an addition but a subtraction: after the Irish War of Independence, the Anglo-Irish Treaty let the southern twenty-six counties leave as the Irish Free State, while six northern counties remained inside the union as Northern Ireland, fixing the territory in its present form. The state kept the name United Kingdom of Great Britain and Ireland for five more years afterward; only the Royal and Parliamentary Titles Act, receiving royal assent on 12 April 1927, renamed it the United Kingdom of Great Britain and Northern Ireland. This atlas dates the United Kingdom's own founding to 1801, the year the name itself was first used for a single state, while carrying the 1707 union, the 1922 partition and the 1927 renaming in the same fact rather than picking one to represent all three.