First off, it shows there are two major networks of fighter aircraft producers and “consumers”. The blue circles & lines show US-made aircraft and those countries them. The red constellation represents Russian aircraft & their buyers. Yellow shows European-made aircraft. Green is Asia.
Click on the image to see a larger version on Martin’s site.
Also, the relative size of the darker-colored circles show the number of aircraft of that type produced (biggest circle is for the F-16). The lighter-colored circles portray a country and how many fighter aircraft in its inventory. Note the relative size of the U.S. circle.
And finally, the silhouettes around the outside show all significant modern fighters fielded around the world today. There are some you may not be familiar with, such as…