Mercator

On 8th April I reported a blunder concerning the moon. I stick my neck out today and offer another fact which might turn out to be false, the trouble with this sort of fact being that one can prove them to be true or false, unlike the soggier facts which are our more normal fare. And I have always been prone to blunders, a tendency which did nothing for my performance at chess.

A few days ago it was alleged to me that the western tip of France, somewhere near Brest, lay just to the west of the western tip of Spain, somewhere near Corunna (the place where our much-loved general Sir John Moore expired). The next step was to ponder about the distortions involved in making maps of spherical bits of earth on flat bits of paper and the fact that one needed to be careful how any particular map was interpreted. Thoughts then turned to the Mercator projection which can generate huge distortions, particularly in higher latitudes. But thoughts which concluded that the Mercator projection preserved northness and westness: that is to say that if place A was to the north of place B, it would be above B in any Mercator projection including the two places and that if place A was to the west of place B, it would be to the left of B in any such projection. This conclusion arising from consideration of the horizontal and vertical straight lines arising from the projection of horizontal and vertical great circles onto the plane of projection. But note that this is not to say that the Mercator projection preserved direction.

Moving onto practical matters, Gmaps tells me that London is around longitude 0, Brest around -5 and Corunna -10. With Czechoslovakia around +15, just to be sure which way round the numbers work. With the fact of Corunna lying to the west of Brest being confirmed by a peek at the Britannia old-style paper atlas, not rich, as it happens, in Mercator projections. They seem to prefer something conic.