Quadrant Charts are a kind of Bubble/Marker Charts which are divided into four equal square sections. Quadrant charts are rather useful when it is necessary to demonstrate the data that contains three measures using an X axis, a Y axis, and a bubble size that represents the value of the third measure.
This chart shows how the popularity of bloggers had been changing during the year. There are two axes, one stands for the followers and second for the comments. Some bloggers have gained more followers than comments, and from starters they moved into the category of those who need more activity - popular, but not interesting enough. Other bloggers have not moved from one category to another.