Leonardo developed a system for representing territories analogous to the one he adopted in his anatomical drawings. Like blood flowing through veins, rivers flow down from mountains, shape valleys, feed lakes, and run through plains, wetting the Earth’s “skin” and subjecting it to continuous change. In his extraordinary cartographic drawings, water is almost always the key element of the illustration.
Waters travel about with perpetual movement from the lowest depths of the sea to the topmost summits of the mountains […] and in its action resembles that of the blood of animals, which is always moving from the sea of the heart and flowing towards the summit of their head and so […] when a vein bursts in the nose, all of the blood rises up to the height where the vein has burst.
Codex Leicester, f. 21v