Monday, 15 July 2013

How long is a mile of coast?

by Richard Neale
“So, how much Welsh coast does the National Trust look after?”

This was the question I was often asked when I started as the Welsh Coast Project Manager.  The answer – as hinted by the title of this blog post – is not quite as simple as you’d think.

Knowing that it was one of the basic pieces of information I needed, I asked – rather too casually, as it turned out – one of our mapping boffins to work it out and the answer came back as 196 miles. 

Suitably impressed, and being prone to a bit of hyperbole, I rounded it up to 200 and started to share the fact with anyone who’d listen.

But it turns out that there was a problem.  I’d omitted to give one vital piece of information to my mapping colleague. That is: what scale I wanted it measured at.   

In my defence, this was before I became aware of something known as the coastline paradox. It turns out that our coastlines are fractal in their nature.  To put it another way, the length of the coastline depends on the method used to measure it. 
The more accurately you measure it, the longer the coast gets!

I could get seriously into the science of this, but suffice to say, the National Trust has been using different scales in different parts of the Trust.  This meant that our coastal statistics have been, well…a bit dodgy.

The time has come for a standardised method to be applied.  And after a fair bit of number-crunching at our head office, the answer has now come through and I can now put the story straight.

  • The National Trust cares for 156.77 miles of Welsh coast (let's say 157). 
  • The total length of the Welsh coast as determined by the same method is 1,465.94 miles
  • This means that the NT cares for 10.7 % of the Welsh coast. 
  • The length of the refreshingly fractal-free Wales Coast Path is 870 miles, meaning that the NT cares for about 18% of land adjacent to the coast path.

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