[Nymph Philosophy] Why the nude female form?

[Linda]

If the nymphs were a representation of the soul, or of geographic locations like Linda puts it, then why did the VMS author(s) use the Balneis or Taccola's diagrams to draw inspiration from? Why not just... draw some random baths? Why the need to copy bath designs and river diagrams specifically from exceedingly rare books, such as De Ingeneis?

Makes no sense to me, if water/bathing was not specifically the objective.

I don't think bathing comes into it, per se. If the Balneis or Taccola's diagrams were popular in a pocket of society that intersected with the makers of the vms, there could be many answers. 

1. The makers saw something and it came to mind while they were drawing, to echo these likenesses somehow for some reason.

2. The makers didn't see or think of any of it, and what seems to be inspiration is simply coincidence.

3. It is a purposeful obfuscation to keep the casual observer from understanding the true nature of the diagrams.

I think the bathing as seen in quire 13 is more of a metaphor for living near/because of water.

In terms of why the nudes? I think it is because it is the bare form everyone is accustomed with, no matter their background, a standard, and the least telling of whence they came, other than the basic European look. No local costumes to give any hints. Bathing would be a good guess whether or not it was seen in a book, though. The nudity, along with them either being in the water or touching it in most cases, would likely bring it to mind anyway. Except that there also is clothing in other parts, I think it is all a progression over a very long period of time.

I also think it would make it understandable to be flustered about having been caught with naked lady pics, however clean and natural they might be, and likely you wouldn't have to explain that you were really hiding secret documents.