What is the perimeter of Great Britain?

Answer 1

Extract from Wikipedia:

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). 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).

Note that the measurement of any coastline is subject to variation depending upon the scale of map used and is an approximation. The smaller the map scale and the smaller the ruler will result in more detail being revealed and thus a greater length. This is referred to as the coastline paradox. A coastline is also fractal - which roughly means that it is self-similar, the same at every scale - the closer the observer looks, the more detail is revealed, leading to a greater overall length.)