D3 Examples - From US Atlas, drawing MD Counties

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<!DOCTYPE html>
<style>
​
.counties :hover {
  fill: red;
}
​
.county-borders {
  fill: none;
  stroke: #fff;
  stroke-width: 0.5px;
  stroke-linejoin: round;
  stroke-linecap: round;
  pointer-events: none;
}
​
</style>
<svg width="960" height="600"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/topojson.v2.min.js"></script>
 <script src="https://d3js.org/d3-scale-chromatic.v1.min.js"></script>
  <script>
     
    var threshold = d3.scaleThreshold()
    .domain([1, 10, 20, 200, 800, 2000, 5000, 10000])
   .range(d3.schemeOrRd[9]);
    
// The original version of this file is here: https://bl.ocks.org/mbostock/4122298
​
var svg = d3.select("svg");
​
var path = d3.geoPath();
​
        
d3.json("https://d3js.org/us-10m.v1.json", function(error, us) {
  if (error) throw error;
​
  
  svg.append("g")
      .attr("class", "counties")
    .selectAll("path")
    .data(topojson.feature(us, us.objects.counties).features)
    .enter().append("path")
      .attr("d", path)
      .on('mouseover', function(d) { console.log('id', d.id) });
​
  svg.append("path")
      .attr("class", "county-borders")
      .attr("d", path(topojson.mesh(us, us.objects.counties, function(a, b) { return a !== b; })));
});
​
   // Remove all counties except the county with FIPS code = 003
  svg.selectAll('path.tract')
      .filter(function(d) { return d.properties.COUNTYFP !== "003" })
      .remove();
  
</script>
​
​
    