Congressional District Topology by mbostock

index.html

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

path {
  stroke-linejoin: round;
  stroke-linecap: round;
}

.land {
  fill: #ddd;
}

.border {
  fill: none;
  stroke: #fff;
}

.graph {
  fill: none;
  stroke: #000;
}

</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 = 600;

var projection = d3.geo.albersUsa()
    .scale(1280)
    .translate([width / 2, height / 2]);

var path = d3.geo.path()
    .projection(projection);

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

queue()
    .defer(d3.json, "/mbostock/raw/4090846/us.json")
    .defer(d3.json, "/mbostock/raw/4090846/us-congress-113.json")
    .await(ready);

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

  var geometryCollection = congress.objects.districts,
      featureCollection = topojson.feature(congress, geometryCollection),
      features = featureCollection.features,
      neighbors = topojson.neighbors(geometryCollection.geometries);

  features.forEach(function(feature, i) {
    feature.centroid = path.centroid(feature);
    if (feature.centroid.some(isNaN)) feature.centroid = null; // off the map
    feature.neighbors = feature.centroid ? neighbors[i]
        .filter(function(j) { return j < i && features[j].centroid; })
        .map(function(j) { return features[j]; }) : [];
  });

  svg.append("path")
      .attr("class", "land")
      .datum(topojson.feature(us, us.objects.land))
      .attr("d", path);

  svg.append("path")
      .attr("class", "border")
      .datum(topojson.mesh(congress, geometryCollection, function(a, b) { return a !== b; }))
      .attr("d", path);

  svg.append("path")
      .attr("class", "graph")
      .datum(d3.merge(features.map(function(a) { return a.neighbors.map(function(b) { return [a, b]; }); })))
      .attr("d", function(d) { return d.map(function(l) { return "M" + l[0].centroid + "L" + l[1].centroid; }).join(""); });
}

d3.select(self.frameElement).style("height", height + "px");

</script>