@heigit great to hear from you, looking forward to meeting in person in Antwerp :)

Regarding the vectorization, I think it's important to tell lines from polygons — at least for waking papers-type of surveying, when we draw missing fences and roads.

Also, the requirement for different colors was weird. Again, that concerns polygons, I think. People usually use pens, blue and black. But then it'd be hard to know what is old and what is new. So a link to a source image might help.