Global Migration in 2015

A Chord Diagram visualization of global migration data from 2015. Data is from the United Nations International Migrant Stock Database. Inspired by:

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <script src="//d3js.org/d3.v4.min.js"></script>
    
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</head>
  <body>
    <script>

// Configuration parameters.
      var width = 960,
          height = 960,
          outerPadding = 150,
          labelPadding = 5,
          chordPadding = 0.03,
          arcThickness = 30,
          opacity = 0.5,
          fadedOpacity = 0.01,
          transitionDuration = 300,
          outerRadius = width / 2 - outerPadding,
          innerRadius = outerRadius - arcThickness,
          valueFormat = d3.format(",");

// DOM Elements.
      var svg = d3.select("body").append("svg")
            .attr("width", width)
            .attr("height", height)
          g = svg.append("g")
            .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")"),
          ribbonsG = g.append("g"),
          groupsG = g.append("g");

// D3 layouts, shapes and scales.
      var ribbon = d3.ribbon()
            .radius(innerRadius),
          chord = d3.chord()
            .padAngle(chordPadding)
            .sortSubgroups(d3.descending),
          arc = d3.arc()
            .innerRadius(innerRadius)
            .outerRadius(outerRadius),
          color = d3.scaleOrdinal()
            .range(d3.schemeCategory20);
      
      var popoverOptions = {
        html : true,
        template: '<div class="popover" role="tooltip"><div class="popover-arrow"></div><div class="popover-content"></div></div>'
      };

// Renders the given data as a chord diagram.
      function render(data){

var matrix = generateMatrix(data),
            chords = chord(matrix);

color.domain(matrix.map(function (d, i){
          return i;
        }));

// Render the ribbons.
        ribbonsG.selectAll("path")
            .data(chords)
          .enter().append("path")
            .attr("class", "ribbon")
            .attr("d", ribbon)
            .style("fill", function(d) {
              return color(d.source.index);
            })
            .style("stroke", function(d) {
              return d3.rgb(color(d.source.index)).darker();
            })
            .style("opacity", opacity)
            .on("mouseenter", function(d){
              var src = matrix.names[d.source.index];
              var dest = matrix.names[d.target.index];
              popoverOptions.content = [
                "<strong>" + src +" to " + dest +"</strong>",
                valueFormat(d.target.value),
                "<br><strong>" + dest +" to " + src +"</strong>",
                valueFormat(d.source.value)
              ].join("<br>");
              $(this).popover(popoverOptions);
              $(this).popover("show");
            }) 
            .on("mouseleave", function (d){
              $(this).popover("hide");
            })

// Scaffold the chord groups.
        var groups = groupsG
          .selectAll("g")
            .data(chords.groups)
          .enter().append("g");

// Render the chord group arcs.
        groups
          .append("path")
            .attr("class", "arc")
            .attr("d", arc)
            .style("fill", function(group) {
              return color(group.index);
            })
            .style("stroke", function(group) {
              return d3.rgb(color(group.index)).darker();
            })
            .style("opacity", opacity)
            .call(groupHover);

// Render the chord group labels.
        var angle = d3.local(),
            flip = d3.local();
        groups
          .append("text")
            .each(function(d) {
              angle.set(this, (d.startAngle + d.endAngle) / 2)
              flip.set(this, angle.get(this) > Math.PI);
            })
            .attr("transform", function(d) {
              return [
                "rotate(" + (angle.get(this) / Math.PI * 180 - 90) + ")",
                "translate(" + (outerRadius + labelPadding) + ")",
                flip.get(this) ? "rotate(180)" : ""
              ].join("");
            })
            .attr("text-anchor", function(d) {
              return flip.get(this) ? "end" : "start";
            })
            .text(function(d) {
              return matrix.names[d.index];
            })
            .attr("alignment-baseline", "central")
            .style("font-family", '"Helvetica Neue", Helvetica')
            .style("font-size", "10pt")
            .style("cursor", "default")
            .call(groupHover);
      }

// Sets up hover interaction to highlight a chord group.
      // Used for both the arcs and the text labels.
      function groupHover(selection){
        selection
          .on("mouseover", function (group){
            g.selectAll(".ribbon")
                .filter(function(ribbon) {
                  return (
                    (ribbon.source.index !== group.index) &&
                    (ribbon.target.index !== group.index)
                  );
                })
              .transition().duration(transitionDuration)
                .style("opacity", fadedOpacity);
          })
          .on("mouseout", function (){
            g.selectAll(".ribbon")
              .transition().duration(transitionDuration)
                .style("opacity", opacity);
          });
      }

// Generates a matrix (2D array) from the given data, which is expected to
      // have fields {origin, destination, count}. The matrix data structure is required
      // for use with the D3 Chord layout.
      function generateMatrix(data){
        var nameToIndex = {},
            names = [],
            matrix = [],
            n = 0, i, j;

function recordName(name){
          if( !(name in nameToIndex) ){
            nameToIndex[name] = n++;
            names.push(name);
          }
        }

data.forEach(function (d){
          recordName(d.origin);
          recordName(d.destination);
        });

for(i = 0; i < n; i++){
          matrix.push([]);
          for(j = 0; j < n; j++){
            matrix[i].push(0);
          }
        }

data.forEach(function (d){
          i = nameToIndex[d.origin];
          j = nameToIndex[d.destination];
          matrix[j][i] = d.count;
        });

matrix.names = names;

return matrix;
      }

d3.csv("migration.csv", type, function (dataForCountries){
        d3.json("hierarchy.json", function (hierarchy){

// Aggretate country data into regional data.
          var dataForRegions = aggregate(dataForCountries, hierarchy)

// Reduce clutter by filtering out links with relatively low counts.
            .filter(function (d){
              return d.count > 10000;
            });

render(dataForRegions);
        });

});

// Parses a single row of the input table.
      function type(d){
        d.count = +d.count;
        return d;
      }

// Aggregates data from countries to regions.
      function aggregate(data, hierarchy){
        var links = {},
            parent = {},
            descendants = d3.hierarchy(hierarchy).descendants();

descendants.forEach(function (node){
          if(node.parent){
            parent[node.data.data.id] = node.parent.data.data.id;
          }
        });

function getLink(origin, destination){
          var key = origin + "|" + destination;
          return (key in links) ? links[key] : (links[key] = {
            origin: origin,
            destination: destination,
            count: 0
          });
        }

data.forEach(function (d){
          getLink(parent[d.origin], parent[d.destination]).count += d.count;

//console.log(d.origin + " is in " + parent[d.origin]);
          //console.log(d.destination + " is in " + parent[d.destination]);
        });

return Object.keys(links).map(function (key){
          return links[key];
        });

}

</script>
  </body>
</html>

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