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January 20, 2006

Rhumb Lines and Map Wars: A Social History of the Mercator Projection - Mark Monmonier

Posted by Jeremy Black

Rhumb Lines and Map Wars: A Social History of the Mercator Projection
by Mark Monmonier
Pp. xiv+242. Chicago: University of Chicago Press, 2004
Hardback, 14.36

Monmonier, Distinguished Professor of Geography at Syracuse University, offers yet another first-rate contribution to the literature on cartography. His focus is one of the most famous projections, that of Gerard Mercator. As Monmonier points out, the popularity of this projection reflected its value for sailors, not least the map's value for plotting an easily followed course that could be marked off with a straight-edge and readily converted to a bearing. Mercator sought to reconcile the navigator's need for a straightforward course with the trade-offs inherent in flattening a globe. Mercator's projection affords negligible distortion on large-scale detailed maps of small areas, but relative size is markedly misrepresented on Mercator charts because of the increased poleward separation of parallels required to straighten out loxodromes.

Monmonier shows how the projection was subsequently employed. It became the cartographic expression of what he terms a hot idea in the late 1590s, when Jodocus Hondius and Edward Wright offered their own versions of Mercator's world. Hondius relied heavily on Wright, who developed a mathematical description as well as tables showing how to position the parallels.

Monmonier then takes the story forward showing how different demands, for example for artillery aiming, influenced the use of projections. For example, before World War I, French artillery officers relied on independent local grids based on Bonne's projection (a nonconformal polyconic variant) and centred on strongholds from which fixed guns might conveniently bombard targets in the region. However, after the angular distortions and awkward discontinuities of the Bonne grids became apparent early in the war, French officials devised a single military grid based on a Lambert conformal conic projection. Directionally accurate long-range artillery and "map firing" also established a need of military surveyors, who relied on conformal projections in helping gun crews get a fix on true north by tying the gun's position into a precisely measured triangulation network.

There is also a first-rate coverage of the Peters projection as part of a more general discussion of the depiction of scale. Monmonier, indeed, argues that population cartograms are fairer than the Peters projection. An excellent book that deserves widespread attention.

Jeremy Black is Professor of History, University of Exeter. Amongst much else, he is the author of Visions of the World: A History of Maps (Mitchell Beazley, 2003), Maps and Politics (Reaktion, 2000), Maps and History: Constructing Images of the Past (Yale University Press, 1997) and The European Question and the National Interest (Social Affairs Unit, 2006).

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Isn't the "New Internationalist" fond of giving away Peters projection maps of the world, as the Mercator projection apparently distorts the relative size of, for instance, Greenland and Brazil? According to the chaps at NI, this is not a mere mathmetical curiosity, but part of the wicked Western plot to marginalise the wretched of the earth etc etc

However the Peters projection, it turns out, has its own flaws...

Posted by: james mcqueen at January 22, 2006 05:43 PM

For a nice equal area projection, much more beautiful than the Peters, may I recommend the Briesemeister Projection? To see CLICK HERE

Posted by: Robert H. Olley at January 31, 2006 05:54 PM
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