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Update: в комментах получил подсказку про источник, где можно прочитать про автора этой карты: The map was the work of Charles Joseph Minard (1781-1870), a French civil engineer who was an inspector-general of bridges and roads, but whose most remembered legacy is in the field of statistical graphics, producing this and other maps in his retirement. This is a translation of the legend at the top of the map