Interpreting Mountains’ Scaling

In a previous post I examined the scale of waterfalls and in yet another post I discussed Johnson’s mountains and rivers comparative. This post draws on both.

The importance of scale is a matter of a map’s purpose. Scale is incredibly important in a plan (plat), where each line must be represented on equal scale so as to ensure accurate delineation of land ownership (think Mason-Dixon Line),

Plan of Mason-Dixon Line, 1768 (Library of Congress).
Plan of Mason-Dixon Line, 1768 (Library of Congress). In such a map, an inaccuracy in location of a line could have substantial legal and political consequences, even military in the case of the Civil War. (Library of Congress).

but less important on a subway (topological) map, where the rider is concerned with the order of the stops more so than the distance between stops (WMATA Map).In the context of a comparative, scale is critical–the whole point of the view is to demonstrate the relative size of geographic features.

With this in mind, Johnson’s choices in scaling are noteworthy.

Comparative Heights of Mountains and Lengths of Rivers
Comparative Heights of Mountains and Lengths of Rivers (Johnson from David Rumsey).

Johnson composed his comparative of 5 panels, one for each of Africa, Asia, Europe, North America, and South America. As an aside, while it’s obvious why Antarctic mountains were omitted, it’s curious that Australian mountains were excluded given that it is one of the 6 inhabited continents, and the largest of the British possessions. The compounding of 5 panels is a logical means of grouping the mountains, facilitating showing more mountains than would be manageable in a single panel. That he chose to use different scales for each panel grabs my attention; by modern data visualization standards it is a mistake at best, if not dishonest, giving the casual reader the impression that the highest peaks of each continent are of about the same altitudes.

Johnson comparative scale analysis.
Scale analysis of the heights of mountains in Johnson’s comparative. Note Everest, second from left, is the index at 1. Mt. Blanc is the most exaggerated at 1.7x, followed by St. Alias at 1.6x (values rounded to one decimal). (Own work).

At issue here is that this choice erodes the comparison between mountains of different continents. One has to wonder whether this was purely an oversight, intentional but innocent for purposes symmetry, or to mislead the reader. The first possibility is self explanatory, requiring no further treatment. On the other hand, the remaining possibilities have the same effect, to confuse the readers’ perceptions of mountain height, but have drastically different implications. An aesthetically motivated scaling decision is questionable–a visualization expert, Johnson no doubt knew that scaling the panels differently would cause readers (those who do not read the heights of mountains) to misperceive the height differences across continents. The plausibility of this explanation hinges on the purpose of the comparative. If it is to show that the heights of mountains vary within continents without regard to intercontinental variance, then perhaps the scaling decision is more likely (and more excusable), but if the purpose is to show the might of mountains across the continents, it is dubious. To that end, if showing the spread in heights across the continents, the map falls short, unless of course, Johnson’s intent was to bamboozle the reader into believing that the mountains of the industrialized world rivaled those of Asia. Whether this was his goal, we do not know.

© Peter Roehrich, 2015.

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