According the Ordnance Survey: “The coastline length around mainland Great Britain is 11,072.76 miles [17,819.88 km].”
However, as the map above shows it’s not really that simple.
The crux of the matter is how many individual vertices you use to make polygons in your map.
In this first map in the series above, Alasdair Rae used 2,282,000 individual vertices, giving him a total distance 11,023 miles (17,739km) or about 49 mile shorter than the Ordnance Survey answer above.
As you can see, once you start removing vertices, the total coastline length starts to shrink rapidly. Once you remove virtually all of them, you’d be left with a shape who’s perimeter would be simply 1,024 miles (1,648 km), although it looks almost nothing like Great Britain.
Conversely, the same process works in reverse, the more individual vertices you use to create your map, the longer the coastline would be. Which means in theory the coastline of Great Britain is infinitely long!
To fully understand how all this works, and for more amazing close-up maps I highly recommend you take some time and check out Alasdair Rae’s blog post How long is the coastline of Great Britain?, which explains in greater detail how this all works.
To learn more about coasts and coastlines have a look at the following books:
- Coastlines: The Story of Our Shore
- Around America: A Tour of Our Magnificent Coastline
- The Fractal Geometry of Nature
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Andy Boylett says
You are wrong. Adding more verticies just assymptotes to the ACTUAL length of the coastline.
Nick says
It does not.
https://en.wikipedia.org/wiki/Coastline_paradox
Jez says
Never heard of a Koch Snowflake/Curve then?
mP says
The other part of the problem is what exactly is the coastline, is it the high tide mark, low tide, somewhere in the middle and what day is this mark taken. If anyone measured one part of the coast one day and returned a year later, they would never get the same measurement because of tides and human assumptions.
R.H.W. Arguile says
The length of a coastline is a matter of convention, though these are useful: the length of the coast at Median High Water Springs is sensible. More useful is the length of a passage at sea from one port/headland or safe anchorage to another. Arguing over a number which affects no one is no doubt fun but it doesn’t make any difference.