D3 Examples - Explaining how a Sankey diagram works

Explaining how a Sankey diagram works

This is an example of a Sankey diagram made using d3.js and the sankey plugin.

A description of how it was put together and techniques for implimenting Sankey diagrams in general with d3.js can be found at d3noob.org or you can download the full text in the D3 Tips and Tricks book (for free) from Leanpub.

The data is sourced from the World Resources Institute (http://www.wri.org/chart/world-greenhouse-gas-emissions-2005). Open in full window for full effect.

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<!DOCTYPE html>
<meta charset="utf-8">
<title>SANKEY Experiment</title>
<style>
​
.node rect {
  cursor: move;
  fill-opacity: .9;
  shape-rendering: crispEdges;
}
​
.node text {
  pointer-events: none;
  text-shadow: 0 1px 0 #fff;
}
​
.link {
  fill: none;
  stroke: #000;
  stroke-opacity: .2;
}
​
.link:hover {
  stroke-opacity: .5;
}
​
</style>
<body>
​
<p id="chart">
​
<script src="https://d3js.org/d3.v3.js"></script>
<script src="sankey.js"></script>
<script>
  
var units = "Widgets";
​
var margin = {top: 10, right: 10, bottom: 10, left: 10},
    width = 1200 - margin.left - margin.right,
    height = 740 - margin.top - margin.bottom;
​
var formatNumber = d3.format(",.0f"),    // zero decimal places
    format = function(d) { return formatNumber(d) + " " + units; },
    color = d3.scale.category20();
​
// append the svg canvas to the page
var svg = d3.select("#chart").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", 
          "translate(" + margin.left + "," + margin.top + ")");
​
// Set the sankey diagram properties
var sankey = d3.sankey()
    .nodeWidth(36)
    .nodePadding(10)
    .size([width, height]);
​
// Creates the path generator based on the diagram properties
var path = sankey.link();
​
// load the data
d3.json("sankeygreenhouse.json", function(error, graph) {
 
//     Create a nodeMap where for each node we specify:
//     dx, dy
//     sourceLinks
//     targetLinks
//     value
//     x and y position
    
    var nodeMap = {};
    graph.nodes.forEach(function(x) { nodeMap[x.name] = x; });
  
//      Recall links in the json contains the following for each link:
//      source
//    target
//    value
  
//   We redefine each link's source and target 
//   by assigning the more detailed object from nodeMap.
  
    graph.links = graph.links.map(function(x) {
      return {
        source: nodeMap[x.source],
        target: nodeMap[x.target],
        value: x.value
      };
    });
​
// Now that we have graph.nodes and graph.links, we use them 
// to set our sankey layout. Further, note that layout is set to the number of iterations the layout has to calculate. For each iteration the layout does a calculation level to avoid collisions. Higher numbers cause a downward drift.
  sankey
      .nodes(graph.nodes)
      .links(graph.links)
      .layout(16);
​
// add in the links
  var link = svg.append("g").selectAll(".link")
      .data(graph.links)
    .enter().append("path")
      .attr("class", "link")
      .attr("d", path)
      .style("stroke-width", function(d) { return Math.max(1, d.dy); })
      .sort(function(a, b) { return b.dy - a.dy; });
​
// add the link titles
  link.append("title")
        .text(function(d) {
            return d.source.name + " → " + 
                d.target.name + "\n" + format(d.value); });
​
// add in the nodes
  var node = svg.append("g").selectAll(".node")
      .data(graph.nodes)
    .enter().append("g")
      .attr("class", "node")
      .attr("transform", function(d) { 
          return "translate(" + d.x + "," + d.y + ")"; })
    .call(d3.behavior.drag()
      .origin(function(d) { return d; })
      .on("dragstart", function() { 
          this.parentNode.appendChild(this); })
      .on("drag", dragmove));
​
// add the rectangles for the nodes
  node.append("rect")
      .attr("height", function(d) { return d.dy; })
      .attr("width", sankey.nodeWidth())
      .style("fill", function(d) { 
          return d.color = color(d.name.replace(/ .*/, "")); })
      .style("stroke", function(d) { 
          return d3.rgb(d.color).darker(2); })
    .append("title")
      .text(function(d) { 
          return d.name + "\n" + format(d.value); });
​
// add in the title for the nodes
  node.append("text")
      .attr("x", -6)
      .attr("y", function(d) { return d.dy / 2; })
      .attr("dy", ".35em")
      .attr("text-anchor", "end")
      .attr("transform", null)
      .text(function(d) { return d.name; })
    .filter(function(d) { return d.x < width / 2; })
      .attr("x", 6 + sankey.nodeWidth())
      .attr("text-anchor", "start");
​
// the function for moving the nodes
  function dragmove(d) {
    d3.select(this).attr("transform", 
        "translate(" + d.x + "," + (
                d.y = Math.max(0, Math.min(height - d.dy, d3.event.y))
            ) + ")");
    sankey.relayout();
    link.attr("d", path);
  }
});
​
</script>
​
</body>
</html>
​
    