The Euro Debt Crisis

Bill Marsh created a nice visual guide to the Euro debt crisis in today’s New York Times using a custom graph layout with directed edges. An alternative approach to visualizing asymmetric relationships among a group of entities is a chord diagram. Chord diagrams don’t show indirect relationships as well, but they better convey the magnitudes of the debt for each country.

This visualization uses two chord diagrams. The diagram on the left emphasizes how much each country lends (creditors); you can see Japan and France are the biggest lenders, but France is also the most exposed by its risky debts to Italy and Greece. The diagram on the right emphasizes how much each country owes (debtors); the United States has by far the largest debt, nearly three times the size of the next-largest debtor, Britain!

Built with D3.js.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.group text {
  font: 11px sans-serif;
  pointer-events: none;
}

.group path {
  stroke: #000;
}

path.chord {
  stroke-width: .75;
  fill-opacity: .75;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var width = 480,
    height = 500,
    outerRadius = Math.min(width, height) / 2 - 4,
    innerRadius = outerRadius - 20;

var format = d3.format(",.3r");

// Square matrices, asynchronously loaded; credits is the transpose of debits.
var debits = [],
    credits = [];

// The chord layout, for computing the angles of chords and groups.
var layout = d3.layout.chord()
    .sortGroups(d3.descending)
    .sortSubgroups(d3.descending)
    .sortChords(d3.descending)
    .padding(.04);

// The color scale, for different categories of “worrisome” risk.
var fill = d3.scale.ordinal()
    .domain([0, 1, 2])
    .range(["#DB704D", "#D2D0C6", "#ECD08D", "#F8EDD3"]);

// The arc generator, for the groups.
var arc = d3.svg.arc()
    .innerRadius(innerRadius)
    .outerRadius(outerRadius);

// The chord generator (quadratic Bézier), for the chords.
var chord = d3.svg.chord()
    .radius(innerRadius);

// Add an SVG element for each diagram, and translate the origin to the center.
var svg = d3.select("body").selectAll("div")
    .data([debits, credits])
  .enter().append("div")
    .style("display", "inline-block")
    .style("width", width + "px")
    .style("height", height + "px")
  .append("svg")
    .attr("width", width)
    .attr("height", height)
  .append("g")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

// Load our data file…
d3.csv("debt.csv", type, function(error, data) {
  if (error) throw error;

var countryByName = d3.map(),
      countryIndex = -1,
      countryByIndex = [];

// Compute a unique index for each country.
  data.forEach(function(d) {
    if (countryByName.has(d.creditor)) d.creditor = countryByName.get(d.creditor);
    else countryByName.set(d.creditor, d.creditor = {name: d.creditor, index: ++countryIndex});
    if (countryByName.has(d.debtor)) d.debtor = countryByName.get(d.debtor);
    else countryByName.set(d.debtor, d.debtor = {name: d.debtor, index: ++countryIndex});
    d.debtor.risk = d.risk;
  });

// Initialize a square matrix of debits and credits.
  for (var i = 0; i <= countryIndex; i++) {
    debits[i] = [];
    credits[i] = [];
    for (var j = 0; j <= countryIndex; j++) {
      debits[i][j] = 0;
      credits[i][j] = 0;
    }
  }

// Populate the matrices, and stash a map from index to country.
  data.forEach(function(d) {
    debits[d.creditor.index][d.debtor.index] = d;
    credits[d.debtor.index][d.creditor.index] = d;
    countryByIndex[d.creditor.index] = d.creditor;
    countryByIndex[d.debtor.index] = d.debtor;
  });

// For each diagram…
  svg.each(function(matrix, j) {
    var svg = d3.select(this);

// Compute the chord layout.
    layout.matrix(matrix);

// Add chords.
    svg.selectAll(".chord")
        .data(layout.chords)
      .enter().append("path")
        .attr("class", "chord")
        .style("fill", function(d) { return fill(d.source.value.risk); })
        .style("stroke", function(d) { return d3.rgb(fill(d.source.value.risk)).darker(); })
        .attr("d", chord)
      .append("title")
        .text(function(d) { return d.source.value.debtor.name + " owes " + d.source.value.creditor.name + " $" + format(d.source.value) + "B."; });

// Add groups.
    var g = svg.selectAll(".group")
        .data(layout.groups)
      .enter().append("g")
        .attr("class", "group");

// Add the group arc.
    g.append("path")
        .style("fill", function(d) { return fill(countryByIndex[d.index].risk); })
        .attr("id", function(d, i) { return "group" + d.index + "-" + j; })
        .attr("d", arc)
      .append("title")
        .text(function(d) { return countryByIndex[d.index].name + " " + (j ? "owes" : "is owed") + " $" + format(d.value) + "B."; });

// Add the group label (but only for large groups, where it will fit).
    // An alternative labeling mechanism would be nice for the small groups.
    g.append("text")
        .attr("x", 6)
        .attr("dy", 15)
        .filter(function(d) { return d.value > 110; })
      .append("textPath")
        .attr("xlink:href", function(d) { return "#group" + d.index + "-" + j; })
        .text(function(d) { return countryByIndex[d.index].name; });
  });
});

function type(d) {
  d.amount = +d.amount;
  d.risk = +d.risk;
  d.valueOf = value; // for chord layout
  return d;
}

function value() {
  return this.amount;
}

</script>

https://d3js.org/d3.v3.min.js