Monthly Archives: May 2018

Boats and Maps

Maps come in all sorts of shapes and sizes and one recent purchase by the Rare Books Section was not one I’d seen before.  The artist’s book The last voyage by Tracey Bush is based on a poem by a seventeenth century wit John Taylor who undertook a journey in a paper boat with two stockfish tied to canes for oars from London to Queenborough on the Isle of Sheppey in Kent.  The map is fashioned into a hand folded paper model of a boat which is accompanied by a booklet with extracts of the poem In praise of the hemp-seed written by Taylor to describe his journey. The booklet and boat are made entirely by hemp paper and are contained in a folder secured by a small piece of hemp rope.

This artistic use of maps is increasing with the popularity of maps as visual objects and you can see them everywhere – mugs, mouse mats and even the former First Lady’s dress. What is it about maps that is so appealing?  Is it the potential for a journey? The depiction of something (generally) real? Or do they just make pretty things to look at? Whatever the draw it has been going on for centuries as can be seen by Leo Belgicus which was first drawn in 1583 by Michaël Eytzinger, an Austrian cartographer.  He depicted the Low Countries as a lion rampant facing east, an image which was popular in various forms for many years.

As was closer to home James Gillray’s caricature of England as an old woman seated on a sea creature.  Otherwise it is the content, rather than the appearance of the map which is more important – who hasn’t seen advertisements for items personalised with a map of a significant location in cufflinks, necklaces and puzzles.

Whatever it is in this age of technology maps remain relevant as practical items (an Ordnance Sheet doesn’t require a mobile phone signal) and an artefact thus still fulfilling the Encyclopaedia Britannica’s definition of cartography as ‘the art and science of graphically representing a geographical area, usually on a flat surface such as a map or chart. It may involve the superimposition of political, cultural, or other non-geographical divisions onto the representation of a geographical area.’

The shortest distance between two points

We came across this map, on a very unusual projection, while processing a previously uncatalogued set of nineteenth century French sea charts produced by the Dépôt des cartes et plans de la marine. Most are standard nautical charts, but this one – part of a set of three – is extraordinary.  The world appears to have been turned inside out; the chart is centred on the central Atlantic, and the land masses are progressively larger and more distorted the further they are from this point. The other two charts represent the Pacific and Indian Oceans in the same way.

The title makes the chart’s purpose clear: ‘Carte pour la navigation par l’arc de grand circle’. A great circle is, technically, the point at which the surface of a sphere intersects with a plane passing through its centre. In practical terms, a great circle drawn on the surface of the Earth between 2 points will be the shortest distance between those points (the Earth is not, of course, a perfect sphere, but it is close enough for this to be of use).

Navigational charts are traditionally drawn on the Mercator projection. This has the great advantage of showing a line of constant bearing (rhumb line) on the Earth’s surface as a straight line on the map. This is the simplest course to navigate, as mariners have known for many hundreds of years, but it is not the shortest. The shortest route is a great circle, and this requires constant adjustment of direction to stay on course. Sailing ships were limited by the challenges of winds and currents, and early steam ships by the need to refuel, but from the 1870s this principle began to have more practical applications. A straight line drawn on this orthodromic chart is a great circle course between the two points it connects, enabling navigators to plan their great circle journeys relatively easily. These charts were published in 1879. 

Charts of this sort do not appear to have passed into common use, and there could be several reasons for this. For one thing, the difficulties of plotting a great circle course are sufficient to outweigh the advantages for all but the longest ocean crossing journeys. Mariners continued to use rhumb line navigation well into the late twentieth century, by which time GPS systems had come into use. When a great circle course was followed, for sea or air travel, it was calculated in advance, sometimes using a chart of this sort. The course would then be plotted onto a Mercator projection chart where it was easier to follow. 

The usefulness of great circles can be seen most clearly on a modern map of long distance air travel. This is why aeroplane routes from, say, London to San Francisco always appear oddly curved when viewed on a map, with the route going much much north than you would expect. This is a great circle course, and the shortest way to connect two distant cities. A demonstration can be seen on this useful site http://demonstrations.wolfram.com/GreatCirclesOnMercatorsChart/.

The charts were created by Gustave Hilleret, a naval lieutenant and teacher at the École supérieure de guerre navale, who also published books on navigation. The projection is the Gnomonic projection with Equatorial aspect; the charts’ Bodleian shelfmark is B1 a.61/1 [39-41].