Your question is kind of vague without any reference to which of the many spot beam maps which are available in this site. (http://satmaps.satelliteguys.us/)
If you are talking about the concentric circles (ovals) in spot beams, that is most likely signal strength with the center circle delivering the strongest signal and the outer circle (or circles depending on the map) delivering successively weaker signals.
If this doesn't answer your question, perhaps a link to the map you are referring to, and a little more description in the the question may help get you the correct answer.