New Scientist magazine has a feature called "The last word", in which readers' questions are answered by other readers.

Recently one reader's question asked what point on earth was farthest from the nearest sea, meaning farthest from any inlet of the world ocean. Rivers don't count, just seas, connected to the world ocean and subject to tides of the whole sea, not just seiches.

A reply was published, calling this point the "continental pole of inaccessibility (CPI)", that said the question was raised in the 1960's when builders of submarine-mounted nuclear missiles wanted to tout an ability to target any point on land from a body of water accessible to the sub fleet.

The reply stated that the point is at 46°17'N, 86°40'E, in northwest China near the Russian border, and went on to say that the nearest arm of the sea was 2848 km away at Tianjin on the Yellow Sea. It stated further, that the sub proponents neglected to mention in promotional literature that as the rockets had barely enough range to cover this distance, that "to strike the pole [of inaccessibility] a large nuclear-powered submarine would practically have to visit Tianjin docks."

What's wrong with that reply to the reader's question?

(In reply to Somewhat confused by FrankM)

In a square the diagonals form the incentre of its incircle.  The incentre is equidistant from each of the square's sides. Distort the square to some other quadrilateral shape. The incentre still gives an incircle which is equidistant from its sides.  Do the same with a triangle.

Consider the coast of Asia as a highly irregular polygon.  Take your "pair of compasses" set at 2848km.  This location is roughly at the intersection of the borders of Russia, Kazakstan, Mongolia and China. Describe a circle.  I am suggesting that the circumference of this circle will not only take in Tianjin but almost certainly engage a location on whatever the sea is that borders that section of Russia somewhat north of that location, a spot on the Caspian Sea [earlier comment I suggested Black Sea], the coast of Pakistan on the Arabian Sea and/or a location on the coast between India and Burma.

Now I have noted 4 possible locations other than Tianjin.  Certainly some of those will be as far from the coords as Tianjin if this location is the said CPI.

Submarines and warheads have nothing to do with the problem other than to cite some authority as to how this location came to nominated.

Posted by brianjn on 2008-05-15 09:45:57