Not to sure if this is intended, or more bug like. (somewhat unlogical to me.)
- Quality spots drop in quality when digging in them.
- If Quality is below 10q, it will not return a resource.
but: even if your not getting anything. It will be counted as a successful dig -> depleting quality spot.
Observed with a clay spot.
Was digging on the q10 level border. And when I digged just on the outside of it, the q10 border reseeded in the same way as if I was digging just inside the q10 border.
---
Ok, no bug. (adjusted title to reflect that)
Knowing why ... is not something that is completely unimportant ... well, at least in my view.