D3 Examples - Choropleth with census api

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
.tract {
  fill: #eee;
}
​
.tract-border, .state-border {
  fill: none;
  stroke: #fff;
  stroke-width: .1px;
}
​
.state-border {
  stroke: #777;
  stroke-width: 1.5px;
}
​
svg {
  display: block;
  margin: auto;
}
​
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script src="//d3js.org/queue.v1.min.js"></script>
​
<script>
var variables = 'B00001_001E,B19013_001E';
var censusKey = '1b948e68b95a0ecf4936f0a6cf17c0e63c82d4de';
var url = 'https://api.census.gov/data/2013/acs5?get=NAME,'+ variables +'&for=tract:*&in=state:40&key=' + censusKey;
​
var width = 960;
var height = 500;
​
var path = d3.geo.path()
  .projection(null);
​
var svg = d3.select("body").append("svg")
  .attr("width", width)
  .attr("height", height);
​
var variableByFIPS = d3.map();
​
var color = d3.scale.threshold()
  .domain([0, 15000, 30000, 45000, 60000, 150000])
  .range( ["#edf8fb","#ccece6","#99d8c9","#66c2a4","#41ae76","#238b45","#005824"] );
​
queue()
  .defer(d3.json, 'ok-tracts.json')
  .defer(d3.json, url)
  .await(ready);
​
function ready(error, ok, data) {
  if (error) throw error;
​
  var tracts = ok.objects.tracts;
​
  tracts.geometries = tracts.geometries
    .filter(function(d) { return (d.properties.TRACTCE / 10000 | 0) !== 99; });
​
  svg.append("g")
    .selectAll("path")
    .data(topojson.feature(ok, tracts).features, function(d) { return d.id; })
    .enter()
    .append("path")
    .attr("class", "tract")
    .attr("d", path);
​
  svg.append("path")
    .attr("class", "tract-border")
    .datum(topojson.mesh(ok, tracts, function(a, b) { return a !== b; }))
    .attr("d", path);
​
  svg.append("path")
    .attr("class", "state-border")
    .datum(topojson.mesh(ok, tracts, function(a, b) { return a === b; }))
    .attr("d", path);
​
  data.forEach(function(d, i) {
    if (i > 0) {
      variableByFIPS.set(d[3] + d[4] + d[5], +d[2]);
    }
  });
​
  d3.selectAll('.tract')
    .style('fill', function(d) { return color( variableByFIPS.get(d.id) ); })
    .append("title")
    .text(function(d) { return d.id + " " + variableByFIPS.get(d.id); });
​
}
​
</script>
​
    