New York Population Density

<!DOCTYPE html>
<meta charset="utf-8">
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>

var width = 960,
    height = 700;

var path = d3.geo.path()
    .projection(null);

var color = d3.scale.threshold()
    .domain([1, 10, 50, 100, 500, 1000, 2000, 5000])
    .range(["#fff7ec", "#fee8c8", "#fdd49e", "#fdbb84", "#fc8d59", "#ef6548", "#d7301f", "#b30000", "#7f0000"]);

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

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

// group tracts by color for faster rendering
  svg.append("g")
      .attr("class", "tract")
    .selectAll("path")
      .data(d3.nest()
        .key(function(d) { return color(d.properties.population / d.properties.area * 2.58999e6); }) // convert square meters to square miles
        .entries(ny.objects.tracts.geometries))
    .enter().append("path")
      .style("fill", function(d) { return d.key; })
      .attr("d", function(d) { return path(topojson.merge(ny, d.values)); });
});

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

</script>

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