Cahill-Keyes map projection

Cahill-Keyes map projection (I modified Waterman butterfly projection in the geo.polyhedron D3 plugin to have incisions at 17° (Thanks Jason for the great inspiration!).

Gene Keyes's first 5 principles:

principal format to an M-shape, joined at south Atlantic
principal dividing meridian to 20° W
incisions at equator and poles at 17°
proportionality of geocells
circular parallels for the polar regions

The last two points are achieved via the custom projection defined by Gene Keyes which I reimplemented in javascript from original Perl program by Mary Jo Graça.

The last principle to take care of is:

re-assemble and attach Antartica. ()

The colouring is inspired (i.e. adapted...ok copied! This is just building on Giants' shoulders: Mike called it For example ;-) from Mike's World Map.

The rendering of Tropic of Cancer/Capricorn and Arctic/Antartic Circle are inspired by Jason's Bartholomew’s Regional Projection.

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

body {
  background: #fcfcfa;
}

.stroke {
  fill: none;
  stroke: #000;
  stroke-width: 1.5px;
}

.fill {
  fill: #ADD8E6;
}

.graticule {
  fill: none;
  stroke: #777;
  stroke-width: .5px;
  stroke-opacity: .5;
}

.parallel {
  fill: none;
  stroke: #000;
  stroke-width: .5px;
  stroke-dasharray: 2,2;
}

.land {
  fill: #none;
  stroke: #000;
  stroke-width: .5px;
}

.country {
  stroke: #000;
  stroke-width: .5px;
}
.boundary {
  fill: none;
  stroke: #fff;
  stroke-width: .5px;
}

</style>
<body>
<script src="d3.v3.1.8.js"></script>
<script src="https://d3js.org/d3.geo.projection.v0.min.js"></script>
<script src="https://espinielli.github.io/pycalcal/d3.geo.polyhedron.js"></script>
<script src="cahill-keyes.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<script>

var width = 960,
    height = 380;

var color = d3.scale.category10();

var ε = 1e-2,
    x0 = 20,   // rotation
    φ0 = 22.5, // Tropic of Cancer
    φ1 = 67.5, // Arctic Circle
    graticule = d3.geo.graticule()
      .majorStep([20, 20])
      .minorStep([10, 10])
      .precision(1.0);

var projection = d3.geo.polyhedron.cahillKeyes()
    .center([0,0])
    .rotate([x0, 0])
    .scale(0.022)
    .translate([width / 2, height / 2 - 60])
    .precision(.1);

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

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

var defs = svg.append("defs");

defs.append("path")
    .datum({type: "Sphere"})
    .attr("id", "sphere")
    .attr("d", path);

defs.append("clipPath")
    .attr("id", "clip")
  .append("use")
    .attr("xlink:href", "#sphere");

svg.append("use")
    .attr("class", "stroke")
    .attr("xlink:href", "#sphere");

svg.append("use")
    .attr("class", "fill")
    .attr("xlink:href", "#sphere");

svg.append("path")
    .datum(graticule)
    .attr("class", "graticule")
    .attr("clip-path", "url(#clip)")
    .attr("d", path);

svg.selectAll("path.parallel")
    .data([
      d3.range(-180, 181, 1).map(function(x) { return [x - x0,  φ0]; }),
      d3.range(-180, 181, 1).map(function(x) { return [x - x0,  φ1]; }),
      d3.range(-180, 181, 1).map(function(x) { return [x - x0, -φ0]; }),
      d3.range(-180, 181, 1).map(function(x) { return [x - x0, -φ1]; }),
      [[-180, 0], [-60, 0], [60, 0], [180, 0]]
    ])
  .enter().append("path")
    .datum(function(d) { return {type: "LineString", coordinates: d}; })
    .attr("class", "parallel")
    .attr("clip-path", "url(#clip)")
    .attr("d", path);

d3.json("https://gist.githubusercontent.com/mbostock/4090846/raw/world-110m.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("clip-path", "url(#clip)")
      .attr("d", path)
      .style("fill", function(d, i) {
        if (d.id == 10 || d.id == 304) // make Antartica and Greenland white
          return d3.rgb("white");
        return color(d.color = d3.max(neighbors[i], function(n) { return countries[n].color; }) + 1 | 0);
      });

svg.insert("path", ".graticule")
      .datum(topojson.mesh(world, world.objects.countries, function(a, b) { return a !== b; }))
      .attr("class", "boundary")
      .attr("clip-path", "url(#clip)")
      .attr("d", path);
});

d3.select(self.frameElement).style("height", height + "px");

</script>

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

Modified http://espinielli.github.io/pycalcal/d3.geo.polyhedron.js to a secure url

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

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

https://espinielli.github.io/pycalcal/d3.geo.polyhedron.js

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