It's unclear how these drawings made it past the institute's proofreaders in the first place.

They may have been inserted only after the maps were approved, when cartographers are asked to apply the proofreaders' final edits.

When the maps were once printed as composite layers of different colors, cartographers could have built the drawings from the interplay of different topographical elements (the naked woman, for example, is composed of a blue line over a green-shaded area).

Hurni also speculates that cartographers could have partitioned their illustrations over the corners of four separate map sheets, although no such example has (yet) been found.