D3 Examples - Bivariate Hexbin Map (IHC Users)

Bivariate Hexbin Map (IHC Users)
Adapted from the d3.hexbin plugin for hexagonal binning on a map with the d3.geo.albersUsa projection. Approximately 4,500 reported locations of IHC users.
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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
path {
  fill: none;
  stroke-linejoin: round;
}
​
.land {
  fill: #ddd;
}
​
.states,
.hexagons path {
  stroke: #fff;
}
​
</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 src="hexbin.min.js"></script>
<script>
​
var dataset = "ihc_users_us_geocoords";
//var dataset = "readme-walmart";
  
var width = 960,
    height = 500,
    parseDate = d3.time.format("%x").parse;
​
var color = d3.time.scale()
    .domain([new Date(1962, 0, 1), new Date(2006, 0, 1)])
    .range(["black", "steelblue"])
    .interpolate(d3.interpolateLab);
​
var hexbin = d3.hexbin()
    .size([width, height])
    .radius(8);
​
var radius = d3.scale.sqrt()
    .domain([0, 12])
    .range([0, 8]);
​
var projection = d3.geo.albers()
    .scale(1000)
    .translate([width / 2, height / 2])
    .precision(.1);
​
var path = d3.geo.path()
    .projection(projection);
​
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, dataset+".tsv")
    .await(ready);
​
function ready(error, us, walmarts) {
  if (error) throw error;
​
  walmarts.forEach(function(d) {
    var p = projection(d);
    d[0] = p[0], d[1] = p[1];
    d.date = parseDate(d.date);
  });
​
  svg.append("path")
      .datum(topojson.feature(us, us.objects.land))
      .attr("class", "land")
      .attr("d", path);
​
  svg.append("path")
      .datum(topojson.mesh(us, us.objects.states, function(a, b) { return a !== b; }))
      .attr("class", "states")
      .attr("d", path);
​
  svg.append("g")
      .attr("class", "hexagons")
    .selectAll("path")
      .data(hexbin(walmarts).sort(function(a, b) { return b.length - a.length; }))
    .enter().append("path")
      .attr("d", function(d) { return hexbin.hexagon(radius(d.length)); })
      .attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; })
      .style("fill", function(d) { return color(d3.median(d, function(d) { return +d.date; })); });
}
​
</script>
​
    