Each dot represents a Member of "Congress"---The House of Representatives (435 of them) and the Senate (100 of them). Republicans are the Red dots and the Democrats are the Blue dots.
Scroll your cursor over a dot and the name of the Congressperson will pop-up. Wish they had the estimated value of their wealth. That would have been helpful.
It is set up in quadrants so you can see the results based on how aggressive Members are in their investment portfolios relative to their wealt. One would presume the more aggressive you are in investing the higher the return on those investment. However, it does not always work out that way.
More info
HERE where I found this infographic. Go
HERE for MUCH MORE interactivity with this graphic. MANY parameters you can set and change. Very informative.