D3 pack layout margin demo

<!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>