World Map

Based on Mike Bostock’s World Map, modified to automatically colour countries such that no adjacent countries share the same colour.

This is done by extracting the topology via TopoJSON and greedily picking colours until the constraint is fulfilled.

See also: Graph coloring on Wikipedia.

Update: Greedily colouring is now performed in a single line, thanks to Mike Bostock!

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

.country {
  fill: #ccc;
  stroke: #fff;
  stroke-width: .5px;
  stroke-linejoin: round;
}

.graticule {
  fill: none;
  stroke: #000;
  stroke-opacity: .3;
  stroke-width: .5px;
}

.graticule.outline {
  stroke: #333;
  stroke-opacity: 1;
  stroke-width: 1.5px;
}

</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script src="https://d3js.org/d3.geo.projection.v0.min.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<script>

var width = 960,
    height = 500;

var projection = d3.geo.kavrayskiy7(),
    color = d3.scale.category20(),
    graticule = d3.geo.graticule();

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

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

svg.append("path")
    .datum(graticule)
    .attr("class", "graticule")
    .attr("d", path);

svg.append("path")
    .datum(graticule.outline)
    .attr("class", "graticule outline")
    .attr("d", path);

d3.json("readme-world.json", function(error, world) {
  var countries = topojson.feature(world, world.objects.countries).features,
      neighbors = topojson.neighbors(world.objects.countries.geometries);

svg.selectAll(".country")
      .data(countries)
    .enter().insert("path", ".graticule")
      .attr("class", "country")
      .attr("d", path)
      .style("fill", function(d, i) { return color(d.color = d3.max(neighbors[i], function(n) { return countries[n].color; }) + 1 | 0); });
});

</script>

Modified http://d3js.org/d3.v3.min.js to a secure url

Modified http://d3js.org/d3.geo.projection.v0.min.js to a secure url

Modified http://d3js.org/topojson.v1.min.js to a secure url

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

https://d3js.org/d3.geo.projection.v0.min.js

https://d3js.org/topojson.v1.min.js