The chart was a personal project created by Matt McKeon, who by day is a researcher at IBM’s Visual Communication Lab (where Fernanda Viegas used to work).
It’s concentric rings show the groups who can see a given slice of information, if you leave the default settings in place. Here’s the service in 2005:
In 2009: 
And now:
via fastcompany.com
This relates to an earlier post and again I encourage your to be wise in how much you put out on the web. I have long since realized that I live a “public life” as a pastor. But this does not mean that my family has to be exposed on the web.
Front Porch Reflections 