Grammatical gender of river names in France

Each watercourse in the French hydrographic network is drawn in a color corresponding to the detected gender of its name: blue, pink and gray, three classes for which no legend is displayed. Blue can reasonably be read as masculine and pink as feminine, with gray probably corresponding to names whose gender could not be determined. The author explains that detection is straightforward for place names containing a common noun (ruisseau, rivière), but less so for proper names without an article, such as the Yonne or the Ain. The map is entertaining and instructive about toponymy, but it lacks a legend and does not specify the method or the data sources.