Yeah, I agree this chart isn't very useful in image format. The JS-based web version, however, is a lot more useful as you can drag your mouse over every path and the tooltips give you each individual metric.

>Also kinda weird that category exists when unknown exists.

I included this category since there are so many characters that are either pure-blood or half-blood (but definitely nothing else), for example: Peter Pettigrew.

>Why is Unknown/No house between Hufflepuff and Ravenclaw?

No reason, I thought it looked better that way.