X axis is the log of the personalized PageRank score of each pubkey, with more trusted on the right, less trusted on the left.

Y axis is the GrapeRank score (specifically, the influence) of each pubkey, with more trusted = higher score.

It appears to me that there is a particular group of bots that can be picked up using this graph that would not be readily identified by using either PageRank or GrapeRank alone.