Threshold Choropleth

This choropleth uses a threshold scale for quantization, mapping arbitrary slices of a continuous domain to discrete values in the range. Unemployment rates ranging from 2 to 10% are quantized into different shades of purple.

var color = d3.scale.threshold()
    .domain([0.02, 0.04, 0.06, 0.08, 0.10])
    .range(["#f2f0f7", "#dadaeb", "#bcbddc", "#9e9ac8", "#756bb1", "#54278f"]);

forked from mbostock's block: Threshold Choropleth

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

.states {
  fill: none;
  stroke: #000;
  stroke-linejoin: round;
}

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

var width = 960,
    height = 500;

var color = d3.scale.threshold()
    .domain([0.02, 0.04, 0.06, 0.08, 0.10])
    .range(["#f2f0f7", "#dadaeb", "#bcbddc", "#9e9ac8", "#756bb1", "#54278f"]);

var path = d3.geo.path();

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

queue()
    .defer(d3.json, "https://gist.githubusercontent.com/mbostock/4090846/raw/d534aba169207548a8a3d670c9c2cc719ff05c47/us.json")
    .defer(d3.tsv, "unemployment.tsv")
    .await(ready);

function ready(error, us, unemployment) {
  if (error) throw error;

var rateById = {};

unemployment.forEach(function(d) { rateById[d.id] = +d.rate; });

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 color(rateById[d.id]); });

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>

https://d3js.org/d3.v3.min.js

https://d3js.org/queue.v1.min.js

https://d3js.org/topojson.v1.min.js