I expect this may excite a number of Voynich writers, though it is not, in fact, an explanation of he Voynich map. What it shows is that ALberti had learned something of the technique by which rhumb-gridded cartes marine had, by then, been created for more than a century.
I add it mainly because in speaking about the patterns created in Juian Bunn’s reduction of the written text, I referred to the colour wheel as possible key for a cipher.
At the time I hadn’t thought to refer to Alberti. He’s a man whose style of drawing is pure Renaissance and has nothing in common with the style in which the Voynich map is drawn.
But he did create cipher, and he did create this ‘rose’ wheel for a depiction of Rome, the images below being two re-creations that I’ve just seen today online. For the associated articles, see the links given on each.