The question about the length of the world’s coastlines is not as easy to answer as it would initially seem. The British mathematician and meteorologist Lewis Fry Richardson was among the first to investigate this phenomenon of the fractal nature of boundary lines in the early twentieth century. The rougher coastlines are, the more of a fractal nature they have and the more difficult it becomes to determine their length since this changes when looking at it using different scales and resolutions.
Richardson’s fellow mathematician, Benoit Mandelbrot, further investigated this phenomenon by looking at the length of the coast of Britain. He explained how the length of a coastline increases the smaller the ruler used for measuring. This has become known as the Coastline Paradox, since it suggests that the length of a coastline theoretically is infinite, or undefinable.
These theoretical notions do not even consider the dynamic nature of planet Earth. The geography of coastlines constantly changes, and sometimes quite significantly within a short period of time. In addition, the large differences in tidal influences add to the difficulty in getting more precise approximations, even with geospatial technologies having improved our capabilities of measuring such phenomena considerably in recent times.
Measuring the length of a coastline therefore is complex, and any induction will remain imperfect. Any statements of length need to be treated with caution as the totals vary depending on the approach used. For example, the World Factbook states the total length of coastlines in the world as 1.16 million kilometres. The World Resources Institute, meanwhile, states a total figure of 1.63 million kilometres in one of its studies.
When comparing the lengths of coastlines of different countries, it is therefore more important to use a consistent mathematical approach to measuring to get a clearer picture of how countries and continents compare globally. For the data used in this month’s cartogram, the estimates from the previously mentioned sources were both taken into account and combined to avoid under-representation of smaller islands but also to get a more complete picture of the varying estimates that exist.
“The fact that we find it almost impossible to determine the real lengths of coasts only adds to the fascination of these areas”
The cartogram shows each country of the world resized according to the total length of its coastline. It is therefore a representation of each country’s share of the world’s coastlines. In addition, the different regions are coloured in shades of blue, with the darkest shade (the Americas) representing the region with the largest share of the world’s coastlines and the lightest shade (Africa) the smallest share. Africa’s relatively small share might look surprising given its land area, but can be explained by it having a much more regular coastline that has far fewer indentations such as inlets, bays or gulfs compared to other regions. Canada, by contrast, has the most complex geography of its coastlines and is therefore the country with the longest coastline regardless of which estimations are used in our calculations.
Coasts are the locations where land meets the world’s oceans. The fact that we find it almost impossible to determine their real lengths only adds to the fascination of these areas where about 44 per cent of the world’s population live within a distance of 150 kilometres.
This was published in the October 2016 edition of Geographical magazine.