title: d3.js: how to create "force-directed graph clusters"
body: <p>I've been exploring the d3.js library, and especially the force directed graph creation. I perused the paper on it by Bostock et al, and noticed the precise type of graph I'm trying to create, basically a force directed graph with color coded regions surrounding groups of a feather.</p>
  
  <p>It's the illustration on 3rd column, 2nd row, here, labelled "force-directed graph clusters":
  <a href="http://vis.stanford.edu/papers/d3" rel="nofollow">http://vis.stanford.edu/papers/d3</a></p>
  
  <p>the code here generates the basic graph:
  <a href="http://mbostock.github.com/d3/ex/force.html" rel="nofollow">http://mbostock.github.com/d3/ex/force.html</a></p>
  
  <p>My question is: what is the code to dynamically generate the region polygons?</p>