D3 pack layout margin demo by larskotthoff

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>

circle {
  fill: rgb(31, 119, 180);
  fill-opacity: .25;
  stroke: rgb(31, 119, 180);
  stroke-width: 1px;
}

.leaf circle {
  fill: #ff7f0e;
  fill-opacity: 1;
}

text {
  font: 10px sans-serif;
}

</style>
<body>
<script src="d3.min.js"></script>
<script>

var diameter = 500,
    format = d3.format(",d");

var pack = d3.layout.pack()
    .margin(10)
    .size([diameter - 4, diameter - 4])
    .value(function(d) { return d.size; });

var svg = d3.select("body").append("svg")
    .attr("width", diameter)
    .attr("height", diameter)
  .append("g")
    .attr("transform", "translate(2,2)");

d3.json("flare.json", function(error, root) {
  if (error) throw error;

  var node = svg.datum(root).selectAll(".node")
      .data(pack.nodes)
    .enter().append("g")
      .attr("class", function(d) { return d.children ? "node" : "leaf node"; })
      .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; });

  node.append("title")
      .text(function(d) { return d.name + (d.children ? "" : ": " + format(d.size)); });

  node.append("circle")
      .attr("r", function(d) { return d.r; });

  node.filter(function(d) { return !d.children; }).append("text")
      .attr("dy", ".3em")
      .style("text-anchor", "middle")
      .text(function(d) { return d.name.substring(0, d.r / 3); });
});

d3.select(self.frameElement).style("height", diameter + "px");

</script>

flare.json

{
 "name": "flare",
 "children": [
  {
   "name": "analytics",
   "children": [
    {
     "name": "cluster",
     "children": [
      {"name": "AgglomerativeCluster", "size": 3938},
      {"name": "HierarchicalCluster", "size": 6714}
     ]
    },
    {
     "name": "graph",
     "children": [
      {"name": "ShortestPaths", "size": 5914},
      {"name": "SpanningTree", "size": 3416}
     ]
    },
    {
     "name": "optimization",
     "children": [
      {"name": "AspectRatioBanker", "size": 7074}
     ]
    }
   ]
  },
  {
   "name": "animate",
   "children": [
    {"name": "Easing", "size": 17010},
    {"name": "FunctionSequence", "size": 5842}
   ]
  }
 ]
}