California Population Density II

A variation of my California population density map using California’s 23,198 block groups rather than its 8,043 tracts. The example exhibits how useful the Census API is: the prepublish script here can automatically grabs the list of counties for the desired state and then the population data for each block group.

forked from mbostock's block: California Population Density II

forked from anonymous's block: California Population Density II

<!DOCTYPE html>
<svg width="960" height="1100"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/d3-scale-chromatic.v1.min.js"></script>
<script src="https://d3js.org/topojson.v2.min.js"></script>
<script>

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

var path = d3.geoPath();

var color = d3.scaleThreshold()
    .domain([1, 10, 50, 200, 500, 1000, 2000, 4000])
    .range(d3.schemeOrRd[9]);

var x = d3.scaleSqrt()
    .domain([0, 4500])
    .rangeRound([440, 950]);

// ALL ABOUT DAT DSCALE DAT DAT SCALE
  var g = svg.append("g")
      .attr("class", "key")
      .attr("transform", "translate(0,40)");

g.selectAll("rect")
    .data(color.range().map(function(d) {
        d = color.invertExtent(d);
        if (d[0] == null) d[0] = x.domain()[0];
        if (d[1] == null) d[1] = x.domain()[1];
        return d;
      }))
    .enter().append("rect")
      .attr("height", 8)
      .attr("x", function(d) { return x(d[0]); })
      .attr("width", function(d) { return x(d[1]) - x(d[0]); })
      .attr("fill", function(d) { return color(d[0]); });

g.append("text")
      .attr("class", "caption")
      .attr("x", x.range()[0])
      .attr("y", -6)
      .attr("fill", "#000")
      .attr("text-anchor", "start")
      .attr("font-weight", "bold")
      .text("Population per square mile");

g.call(d3.axisBottom(x)
      .tickSize(13)
      .tickValues(color.domain()))
    .select(".domain")
      .remove();

d3.json("topo.json", function(error, topology) {
  if (error) throw error;
	
//   console.log(topojson.feature(topology, topology.objects.blockgroups));
  
  // colour coded politicl divisions
  svg.append("g")
    .selectAll("path")
    .data(topojson.feature(topology, topology.objects.blockgroups).features)
    .enter().append("path")
      .attr("fill", function(d) { return d3.schemeOrRd[9][d.id]; })
      .attr("d", path);

// draws borders
  svg.append("path")
      .datum(topojson.feature(topology, topology.objects.counties))
      .attr("fill", "none")
      .attr("stroke", "#000")
      .attr("stroke-opacity", 0.3)
      .attr("d", path);
});

</script>

https://d3js.org/d3.v4.min.js

https://d3js.org/d3-scale-chromatic.v1.min.js

https://d3js.org/topojson.v2.min.js