Counties of the United Kingdom
The counties of the United Kingdom are subnational divisions of the United Kingdom, used for the purposes of administrative, geographical and political demarcation. The older term, shire is historically equivalent to county. By the Middle Ages, county had become established as the unit of local government, at least in England. By the early 17th century, all of England, Wales, Scotland, and Ireland had been separated into counties. In Scotland shire was the only term used until after the Act of Union 1707.
Since the early 19th century, counties have been adapted to meet new administrative and political requirements, and the word county (often with a qualifier) has been used in different senses for different purposes. In some areas of England and Wales, counties still perform the functions of modern local government. In other parts of the United Kingdom, especially within large metropolitan areas, they have been replaced with alternative unitary authorities, which are considered 'county level' authorities. Today, these have largely replaced the historic county corporate entities granted self-governance with county government powers. Today, in addition to local government counties, every part of the United Kingdom lies within the historic counties which have formed geographic and cultural units since the Middle Ages.
Additionally, there are vice-counties, which are geographic areas based on the historic counties, and used in scientific data gathering. Their purpose is to maintain the stability of the geographic area for scientific studies, and thus ignore changes in political demarcations.