New York Map

<!DOCTYPE html>
<meta charset='utf-8'>
<title>NY Counties</title>
<style>
body {
  margin: 0;
  background-color: #eee;
}

.info {
  position: absolute;
  top: 50px;
  left: 50px;
}
</style>
<div class="info"></div>
<svg width="960" height="500" stroke="#000" stroke-linejoin="round" stroke-linecap="round">
  <defs>
    <filter id="blur">
      <feGaussianBlur stdDeviation="5"></feGaussianBlur>
    </filter>
  </defs>
</svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://unpkg.com/topojson-client@3"></script>
<script>

// This demo modified slightly from https://bl.ocks.org/mbostock/4108203

var svg = d3.select("svg");

var defs = svg.select("defs");

// New York central state plane, EPSG: 2829
// (central meridian = - 76.5833..., latitute of origin = 40)
var projection = d3.geoTransverseMercator()
        .rotate([76 + 35 / 60, - 40]);

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

// Load the topojson and the population data
  var counties = "https://raw.githubusercontent.com/umbcvis/classes/master/class-14/counties.json";
  var population = "https://raw.githubusercontent.com/umbcvis/classes/master/class-14/population.json";
d3.queue()
    .defer(d3.json, counties)
    .defer(d3.json, population)
    .await(ready);

// Wait for the data to arrive, then begin processing
function ready(error, us, population) {
  if (error) throw error;

// Make the population data easy to query by FIPS code
  var data = d3.map();
  population.forEach(function(d, i) {
    if (i === 0) return;  // skip the first line in the population data
    data.set(d[1] + d[2], +d[0]);
  });

// Convert the topojson to an array of GeoJSON counties
  var counties = topojson.feature(us, us.objects.counties);

// Get NY counties as array of GeoJSON features
  var newyork = counties.features.filter(function(d) { return d.properties.STATEFP === '36' })

// Inspect the data in the developer console
  console.log('here is the population data:', population[0], population[1]);
  console.log('here is one of the counties:', newyork[0]);

projection.fitExtent([[10,10],[960 - 20, 500 - 20]], { type: "FeatureCollection", features: newyork });

// Plot the boundary of the US
  svg.append("path")
      .attr("id", "nation")
      .attr("d", path(topojson.merge(us, us.objects.counties.geometries)))
      .attr("stroke-width", 2)

// Drop-shadow styling (this is blurred shadow)
  svg.append("use")
      .attr("xlink:href", "#nation")
      .attr("fill-opacity", 0.2)
      .attr("filter", "url(#blur)");

// Drop-shadow styling (this is white overlay)
  svg.append("use")
      .attr("xlink:href", "#nation")
      .attr("fill", "#fff");

// Plot the state boundaries
  svg.append("path")
      .attr("stroke-width", 1)
      .attr("fill", "none")
      .attr("d", path(topojson.mesh(us, us.objects.counties, function(a, b) { return a.properties.STATEFP !== b.properties.STATEFP; })));

// Plot the individual counties
  svg.selectAll('path.county')
      .data( newyork )
    .enter().append("path")
      .attr("d", path)
      .attr("class", "county")
      .attr("fill", "#fff")
      .attr("stroke", "#aaa")
      .attr("stroke-width", 0.5)
      .on('mouseover', function(d, i) {
        console.log('mouseover:', i, d);
        d3.select(this).attr('fill', 'crimson');
        d3.select(".info").html(d.properties.NAME + " County"
                              + "<br>Population: "
                             + d3.format(",d")(data.get(d.properties.GEOID)))
      })
      .on('mouseout', function(d) {
        d3.select(this).attr('fill', '#fff');
        d3.select(".info").html("")
      });
}

</script>

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

https://unpkg.com/topojson-client@3