Coastline of the United Kingdom

The coastline of the United Kingdom is formed by a variety of natural features including islands, bays, headlands and peninsulas. It consists of the coastline of the island of Great Britain and the north-east coast of the island of Ireland, as well as a large number of much smaller islands. Much of the coastline is accessible and quite varied in geography and habitats. Large stretches have been designated areas of natural beauty, notably the Jurassic Coast and the Heritage Coast.

The mapping authority for the United Kingdom, the Ordnance Survey, records the coastline of the main island, Great Britain, as 11,072.76 miles rounding to 11,073 miles (17,820 km). The British Cartographic Society points out that "The true answer is: it depends!". If the larger islands are added the coastline, as measured by the standard method at Mean High Water Mark, rises to about 19,491 miles (31,368 km). According to the CIA Factbook, the length of the UK coastline is around 12,429 km or 7,723 miles, although no details are provided about how this figure was calculated. On the basis of EU Marine Strategy Framework Directive boundaries, the UK coastline can be divided into the eastern, Greater North Sea section, which using 1km2 box counts and including islands is 4,994 km, and a western Celtic Seas coastline, which using the same measurement approach and including Northern Ireland is 14,201 km.

Furthermore, the measurement of any coastline is subject to variation depending upon the scale of map used. It is a meaningless statistic without knowing the scale of the map being used and the accuracy of the measurement. A larger map scale and smaller unit of measure will result in more detail being revealed and measured and thus a greater length. And because the resultant length increases exponentially faster than the increase of scale of measurement, there is no such thing as "an approximate answer" to this question. This is referred to as the coastline paradox. A coastline is fractal-like — which means that it has self-similar properties, similar at every scale — therefore the closer the observer looks, the more detail is revealed, leading to a greater overall length.

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