Call yourself a Geographer ?

If so, can you tell  me what’s wrong with this answer taken from a question asked in the House of Lords via the excellent theyworkforyou website…

UK: Coastline

House of Lords

Written answers and statements, 23 June 2010

Lord Laird (Crossbench)

To ask Her Majesty’s Government what is the length of the United Kingdom coastline in miles at (a) low, and (b) high, tide; and what are the lengths of the coastlines of (a) England, (b) Northern Ireland, (c) Scotland, and (d) Wales.

Baroness Hanham (Parliamentary Under Secretary of State, Communities and Local Government; Conservative)

Information provided by Ordnance Survey for Great Britain and by Land and Property Services, an agency of the Department of Finance and Personnel for Northern Ireland, indicates that the lengths of the coastlines at mean high water (MHW) and mean low water (MLW), (mean high water springs [ordinary spring tides] and mean low water springs in Scotland) are:

Country Length of Coastline at Mean Low Water (MLW) [Miles] Length of Coastline at Mean High Water (MHW) [Miles]
England 8,417 9,462
Northern Ireland 620 542
Scotland 14,675 13,186
Wales 2,323 1,999
United Kingdom 26,035 25,189

These coastal lengths include all offshore islands, and land areas which are above MLW.

The precise length of coastlines will vary from time to time due to natural and gradual changes arising from coastal erosion and silt deposition.

Written and submitted from Warsaw Airport (52.177N, 20.974E)


  1. Thierry Gregorius

    Naturally they have never heard of fractals. If they had, they would know that it is impossible to tell the length of a coastline because it depends on the scale you are looking at.

  2. Richard Treves

    Good spotting Ed, fractals needs a caveat more than erosion does.

    While we’re being Geeky geographers, fascinated to see the coast of England at high water is longer than at low water and its only England that is like this. Initially I thought it was a mistake but it is actually possible.

  3. Peter Yard

    When the tide is high we send our troops into another country! Thus artificially extending the coastline for statistics purposes. When no coastline exists we get the Conservatives in to peform some creative number crunching.

  4. Bill Oates

    Now the interesting question: how long does UKHO (or Seazone for that matter) reckon the coast is. Also what about the Crown Estates? Am I wrong in thinking that the Queen owns this bit? Perhaps an urban myth….

  5. Ray

    The area of land is greater during a low tide – so it doesn’t make sense that the length of coastline for England would be LESS than during a high tide (when the area is less than during a high tide).

  6. Steve Edge

    A quality answer always depends on the quality of the question. In my (now past) professional job, I was asked to give the lengths of the coastline for each English county, based on OS’s MHW. A few raised eyebrows when Nottinghamshire turned in a longer coastline than West Sussex…

  7. David

    Ah, but of course it can. At high tide many sections of land will become islands therefore giving the possibility of increasing the overall length of coastline. I’m not saying this is correct, but surely it is possible…?

  8. Steve Edge

    David is right. There’s another situation which may contribute to odd answers – where MLW is coincident with MHW, the OS omit MLW info, even at large scales. It all shows the dangers of merely adding up numbers in a GI dataset.

  9. Richard Treves

    Re the length of the coast at high tide, it’s possible that its longer because you could generate many inlets that didn’t exist at low tide, and, as David notes, you could also genearate more islands

  10. Laurence Penney

    Hypothetically, a given length of MHW coastline, being shaped by the combined effects of wind, sea and river, could be typically longer than the same length of MLW coastline, the latter being shaped only by the sea and hence smoother. The effect is probably greater if we consider fractal coastlines.

  11. Bruce

    It makes perfect sense. At low tide the coastline is nice and straight along the sand, smooths out all the crinkles. When tide is high, the water comes up to all those crinkles in the coastline and hence the coastline is longer. Of course, the area of the country increases massively at low water I imagine. This makes perfect sense to me, I don’t see what the problem is???

  12. sweavo

    Ah, well spotted David! I was trying to create some scenario like that to explain the figures but didn’t think of idland-tops. Nice!

  13. Christian Pauschert

    I think it is plausible. But depends on the nature of the country looking at. I’ve been to England only twice but I have a coast with a rocky cliff in mind that stands on a sandy beach (or gravel) that is exposed at low tide and flooded at high tide. At low tide you have a straight line of coast on the sand at high tide when the water level reaches to the rocks every edge and curve in it adds up to the coastline.
    A larger circumference is not necessarly linked to a large area. That is very basic geometry.

  14. Stu Mitchell

    I was trying to think if there were any coastal features in particular that give rise to this. For instance, is there anything at low tide which means that the perimeter (?) around it is less? If the low-tide-means-straight-lines is true, it should be true across NI, Wales and Scotland too. Given that the Thames and Severn are the largest estuaries, I wondered if it was to do with this and the prevalence of sand (which gives a straight coastline at low tide) vs. cliffs (which may give the same answer – if the sea always meets cliffs).

    But in the end, I’ve calculated the ratios of each, and they’re roughly 1.12-1.14. Except for England, which is -1.12. So my guess is that it’s a typo.

  15. Richard Cornish

    The length of coastline is entirely dependent of the granularity of measurement, so varies depending on the size of your ruler. For every division by 2 of the length of measurement the coastline increases in proportion by a factor of two. Any locus is made of a number of datum points, the greater the frequency of datum points the greater number of measurements between them. As demonstrated by those fine chaps on BBC’s Coast.

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  17. Tom Williams

    Clearly it depends : Faversham Creek for example, at very low tide the sea water stretches only a few metres up the mouth of the creek, whereas at high tide the sea water goes inland a few miles. All depends what you consider the coastline the minimum and maximum intertidal zone? what saline measurement is used for brackish water? The answer is a lot more the closer you look and each section will have more or less coast depending on the height of the tide, it may actually be an impossible question to answer without a lot of caveats.

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