Map Loupe by syntagmatic

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>
body {
  margin: 0;
  width: 960px;
}

.counties {
  fill: none;
}

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

.q0-9 { fill:rgb(247,251,255); }
.q1-9 { fill:rgb(222,235,247); }
.q2-9 { fill:rgb(198,219,239); }
.q3-9 { fill:rgb(158,202,225); }
.q4-9 { fill:rgb(107,174,214); }
.q5-9 { fill:rgb(66,146,198); }
.q6-9 { fill:rgb(33,113,181); }
.q7-9 { fill:rgb(8,81,156); }
.q8-9 { fill:rgb(8,48,107); }

</style>
<body>
<div id="main" style="float: left;"></div>
<div id="zoom" style="float: left;"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/queue-async/1.0.7/queue.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/topojson/1.6.19/topojson.min.js"></script>
<script>

var width = 480,
    height = 500;

var rateById = d3.map();

var quantile = d3.scale.quantile()
    .range(d3.range(9).map(function(i) { return "q" + i + "-9"; }));

var projection = d3.geo.albersUsa()
    .scale(680)
    .translate([width / 2, height / 2]);

var projectionzoom = d3.geo.albersUsa()
    .scale(4000)
    .translate([width / 2, height / 2]);

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

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

var svg = d3.select("#main").append("svg")
    .attr("width", width)
    .attr("height", height)
    .on("mouseover", function() {
      var point = projectionzoom(projection.invert(d3.mouse(this))); 
      svgzoom.attr("transform", "translate(" + (width/2-point[0]) + "," + (height/2-point[1]) + ")")
    });

var svgzoom = d3.select("#zoom").append("svg")
    .attr("width", width)
    .attr("height", height)
    .append("g");

queue()
    .defer(d3.json, "/mbostock/raw/4090846/us.json")
    .defer(d3.tsv, "unemployment.tsv", function(d) { rateById.set(d.id, +d.rate); })
    .await(ready);

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

  quantile.domain(rateById.values());

  svg.append("rect")
    .style("fill", "#fff")
    .attr("width", width)
    .attr("height", height)

  svg.append("g")
      .attr("class", "counties")
    .selectAll("path")
      .data(topojson.feature(us, us.objects.counties).features)
    .enter().append("path")
      .attr("class", function(d) { return quantile(rateById.get(d.id)); })
      .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);

  svgzoom.append("rect")
    .style("fill", "#fff")
    .attr("width", width)
    .attr("height", height)

  svgzoom.append("g")
      .attr("class", "counties")
    .selectAll("path")
      .data(topojson.feature(us, us.objects.counties).features)
    .enter().append("path")
      .attr("class", function(d) { return quantile(rateById.get(d.id)); })
      .attr("d", pathzoom);

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

}

</script>