My Final project

<!DOCTYPE html>
<meta charset='utf-8'>
<title>Class Project</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" fill="none" stroke="#000" stroke-linejoin="round" stroke-linecap="round">
<defs>
    <filter id="blur">
      <feGaussianBlur stdDeviation="5"></feGaussianBlur>
    </filter>
  </defs>
</svg>

// add title
  var svg = d3.select("svg");
var layer1 = svg.append("g");
var path = d3.geoPath();
  var width;
  var text = svg.append('text')
 .attr('width', width)   
 .attr('x', "14em" )
    .attr('y', "1em")
    .style('font-size', '1.5em')
    .style('text-anchor', 'middle')
    .text('Population of Newyork under 5 years')
  	.style("fill", "black")

// 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);

var threshold = d3.scaleThreshold()
    .domain([1, 2, 4, 5, 6, 8, 10 ])
    .range(d3.schemeOrRd[8]);

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

var svg = d3.select("svg").append("g")
    .attr('transform', 'scale(4)translate(-700, -100)');

var path = d3.geoPath();

var filename = "https://raw.githubusercontent.com/qaisarmehmood/umbcvis/master/Newyork.population%20Data.csv"

d3.queue()
    .defer(d3.json,"https://unpkg.com/us-atlas@1/us/10m.json")
    .defer(d3.csv, filename)
    .await(ready);
  addLegend();

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

console.log('here is the csv data:', csv);

var counties = topojson.feature(us, us.objects.counties).features;

// Examine one of the county features in the developer console.
  // The "id" attribute is a 5-digit GEOID (state + county).
  // See: https://www.census.gov/geo/reference/geoidentifiers.html
  console.log(counties[0]);

// NEW: Create a d3.map() so we can query CSV data by "id" = FIPS code
   var data = d3.map();
  csv.forEach(function(d) { data.set(d.FIPS, d)})
  newyork = counties.filter(function(d) { return d.id.slice(0,2) === "36"; })
  svg.append("g").selectAll("path")
      .data(newyork)
  	.enter().append ("path")
      .attr("d", path)
        .style("fill", function(d) { return threshold(data.get(d.id) ? data.get(d.id).Percent : null);  })

// Get New York counties
 // Get New York counties
  //newyork = counties.filter(function(d) { return d.id.slice(0,2) === "36"; })
   svg.selectAll('path.county')
      .data( newyork )
    .enter().append("path")
      .attr("d", path)
      .attr("class", "county")
      .attr("stroke", "#aaa")
      .attr("stroke-width", 1)  
    // .attr("fill", function(d) { return threshold(d.county); })
    .on('mouseover', function(d, i) {
     d3.select(this).attr('stroke-width', 2).raise()
          console.log(d.id, data.get(d.id)); 
          d3.select(".info").html(data.get(d.id)["County Name"] +
                           "<br>Percent: "
                              + d3.format(",d")(data.get(d.id).Percent))
    
      })
      .on('mouseout', function(d) {
      //d3.select(this).attr('fill', '#fff');
        d3.select(".info").html("")
        d3.select(this).attr('stroke-width', 0.5)
      });

svg.append("path")
      .attr("stroke-width", 0.5)
      .attr("d", path(topojson.mesh(us, us.objects.states, function(a, b) { return a !== b; })));

svg.append("path")
      .attr("d", path(topojson.feature(us, us.objects.nation)));

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

var formatNumber = d3.format("d");

var x = d3.scalePow().exponent('.15')
      .domain([1, 10])
      .range([0, 300]);

var xAxis = d3.axisBottom(x)
      .tickSize(13)
      .tickValues(threshold.domain())
      .tickFormat(formatNumber)

var g = d3.select('svg').append('g')
      .attr('transform', 'translate(50, 120)')
      .call(xAxis);

g.select(".domain")
      .remove();

g.selectAll("rect")
    .data(threshold.range().map(function(color) {
      var d = threshold.invertExtent(color);
      if (d[0] == null) d[0] = x.domain()[0];
      if (d[1] == null) d[1] = x.domain()[1];
      return d;
    }))
    .enter().insert("rect", ".tick")
      .attr("height", 8)
      .attr("x", function(d) { return x(d[0]); })
      .attr("width", function(d) { return x(d[1]) - x(d[0]); })
      .attr("fill", function(d) { return threshold(d[0]); });

g.append("text")
      .attr("fill", "#000")
      .attr("font-weight", "bold")
      .attr("text-anchor", "start")
      .attr("y", -6)
      .text("Percentage of under 5 in a county");
}

</script>

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

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

https://d3js.org/d3-scale-chromatic.v1.min.js