Choropleth

Source: Bureau of Labor Statistics, Census Bureau

This choropleth shows unemployment rates as of August, 2016 with a threshold scale. I employed a mix of command-line tools to transform the fixed-width text file into a CSV, including dsv2dsv:

cat <(echo "id,rate") \
  <(tail -n +7 laucntycur14.txt \
    | grep 'Aug-16' \
    | cut -b 21-22,28-30,129-133 \
    | tr -s ' ' \
    | dsv2dsv -r ' ') \
  | csv2tsv \
  > unemployment.tsv

forked from mbostock's block: Choropleth

forked from zanarmstrong's block: Choropleth

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

.counties {
  fill: none;
}

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

</style>
<svg width="960" height="600"></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>
  
// goal: change the color scale
var color = d3.scaleLinear()
		.domain([2, 4, 6, 50])
    .range(["gold", "white", "white","black"]);
 
// array gets populated with unemployment rates
// could use mungeData to extract median, etc
var rateArray = [];

var fillFunction = function(d) {
  console.log(d.rate = unemployment.get(d.id))
  // d.id is the id of the county
  return color(d.rate = unemployment.get(d.id));
}
  
///////////////////////////////

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

var unemployment = d3.map();

var path = d3.geoPath();

var g = svg.append("g")
    .attr("class", "key")
    .attr("transform","translate(0,40)");

// get data for us county shapes and unemployment data
d3.queue()
    .defer(d3.json, "https://d3js.org/us-10m.v1.json")
    .defer(d3.tsv, "unemployment.tsv", function(d) {
  // parse tsv
  rateArray.push(+d.rate)
  unemployment.set(d.id, +d.rate); 
})
    .await(ready);

function ready(error, us) {
  if (error) throw error;
  
  // unemployment data is a dictionary of county id to unemployment rate

// draw us counties
  svg.append("g")
      .attr("class", "counties")
    .selectAll("path")
    .data(topojson.feature(us, us.objects.counties).features)
    .enter().append("path")
  // fill determines color
      .attr("fill", fillFunction)
      .attr("d", path)
    .append("title")
      .text(function(d) { return d.rate + "%"; });

svg.append("path")
      .datum(topojson.mesh(us, us.objects.states, function(a, b) { return a !== b; }))
      .attr("class", "states")
      .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