Area Choropleth by mbostock

index.html

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

.states {
  fill: none;
  stroke: #fff;
  stroke-linejoin: round;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>

var width = 960,
    height = 500;

var fill = d3.scale.log()
    .domain([10, 500])
    .range(["brown", "steelblue"]);

var path = d3.geo.path();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

d3.json("/mbostock/raw/4090846/us.json", function(error, us) {
  if (error) throw error;

  svg.append("g")
      .attr("class", "counties")
    .selectAll("path")
      .data(topojson.feature(us, us.objects.counties).features)
    .enter().append("path")
      .attr("d", path)
      .style("fill", function(d) { return fill(path.area(d)); });

  svg.append("path")
      .datum(topojson.mesh(us, us.objects.states, function(a, b) { return a.id !== b.id; }))
      .attr("class", "states")
      .attr("d", path);
});

</script>