The Great Lakes are North America’s ecological crown jewels. Providing sandy beach and marsh shoreline as well as littoral, pelagic, and benthic habitats, and the largest freshwater lake system on the planet containing 21% of freshwater, the lakes support diverse life both in the water and within the watershed. The St Lawrence River supports still more riverine life. Their distinct shapes are visible from space, and their importance extends further to human populations, commerce, and more. With these substantial roles in mind, I am sure to look at the Great Lakes when inspecting a comparative view, either one of lakes or a rivers piece that includes lakes.
The Great Lakes take several morphologies on comparative maps. I use Lake Michigan as my benchmark and most of this post will focus on Lake Michigan, but it is not unique in its shape evolving. In lakes comparatives (some of rivers, too) dating to around 1850 or later, Lake Michigan takes its characteristic kidney bean shape; it is shown looking more like an eggplant prior to that. Further, on most rivers comparative views, its shape is all over the map (pun intended).
Lakes Comparative Views
Lakes comparative views are less common than their mountains and rivers cousins. That said, with even a few we can evaluate the differences among them. The most apparent difference to an American reader is the shape of Lake Michigan over time. As mentioned above, it goes from eggplant to bean shape over the course of twenty or so years.
Knowing that the bean shape is true, you may wonder whether the cartographer simply made a mistake. I can dismiss this out of hand as maps contemporary to the said comparative also show the lake as straight. The other possibility is that the cartographer got it right vis-a-vis the information available at the time, and it was a true cartographic error (an inaccuracy in the map due to mistaken information available at the time); this is the most parsimonious explanation.
A review of later maps alongside other sources explains the change. In 1836 Michigan joined the Union and Wisconsin in 1848. These admissions required precise measurements of boundaries and a survey was performed, yielding the modern understanding of the lake. The Michigan Geological Survey, authorized by the state legislature on the day of its formation in 1836, is a candidate (still my hypothesis, I’m researching now to confirm) for the source of these revised maps.
Lakes on Rivers Comparatives
Lakes appearing on rivers comparative maps run the gamut from faithful renderings to examples of great license. Such is the case with depictions of Lake Michigan and there’s a simple reason for this. Rivers comparative maps are concerned with the length, and to some extent other physical characteristics; lakes, especially tangential ones, are of low priority. Considering the Lawrententian system extends from Duluth, through the great lakes, and along the St Lawrence to the Atlantic, Lake Michigan is not on the longest path. Any inclusion of it on a rivers comparative is more contextual than critical. To that end, cartographers can be excused for taking liberties with its orientation, size, or showing it at all.
The reader will “get it” when reading one of these maps as they are coming in with the understanding that they are seeing rivers rather than lakes. This isn’t too say that showing lakes doesn’t add value, it does. The lakes aid the reader in identifying the river system, understanding the watershed, and appreciating the human population the system sports. When a river system’s orientation is changed, say so that it flows to the edge of the page, the lakes, also reoriented, assist the reader in realizing this.
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© Peter Roehrich, 2016