croogie
4/6/2015 - 11:39 AM

D3: Non-Contiguous Cartogram

D3: Non-Contiguous Cartogram

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<!DOCTYPE html>
<meta charset="utf-8">
<title>Non-Contiguous Cartogram</title>
<style>

.land {
  fill: #fff;
  stroke: #ccc;
}

.state {
  fill: #ccc;
  stroke: #666;
}

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

// Ratio of Obese (BMI >= 30) in U.S. Adults, CDC 2008
var valueById = [
   NaN, .187, .198,  NaN, .133, .175, .151,  NaN, .100, .125,
  .171,  NaN, .172, .133,  NaN, .108, .142, .167, .201, .175,
  .159, .169, .177, .141, .163, .117, .182, .153, .195, .189,
  .134, .163, .133, .151, .145, .130, .139, .169, .164, .175,
  .135, .152, .169,  NaN, .132, .167, .139, .184, .159, .140,
  .146, .157,  NaN, .139, .183, .160, .143
];

var path = d3.geo.path();

var svg = d3.select("body").append("svg")
    .attr("width", 960)
    .attr("height", 500);

d3.json("/d/4090846/us.json", function(error, us) {
  svg.append("path")
      .datum(topojson.feature(us, us.objects.land))
      .attr("class", "land")
      .attr("d", path);

  svg.selectAll(".state")
      .data(topojson.feature(us, us.objects.states).features)
    .enter().append("path")
      .attr("class", "state")
      .attr("d", path)
      .attr("transform", function(d) {
        var centroid = path.centroid(d),
            x = centroid[0],
            y = centroid[1];
        return "translate(" + x + "," + y + ")"
            + "scale(" + Math.sqrt(valueById[d.id] * 5 || 0) + ")"
            + "translate(" + -x + "," + -y + ")";
      })
      .style("stroke-width", function(d) {
        return 1 / Math.sqrt(valueById[d.id] * 5 || 1);
      });
});

</script>
README.md
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Unlike choropleth maps, cartograms encode data using area rather than color, resulting in distorted geographic boundaries. In this example, states are rescaled around their centroid, preserving local shape but not topology. Inspired by Zachary Johnson. Non-continguous cartogram design invented by Judy Olsen. U.S. state and county boundaries from the U.S. Census Bureau, simplified using GDAL and MapShaper.