Albers USA

A visual explanation of how D3’s Albers USA composite projection divides the earth into four areas, similar to a k-d tree. This only applies to D3 versions prior to 3.1.8, which rewrote the Albers USA projection to use clipping, offering greater flexibility. (See Albers USA + PR for a related example that preserves Puerto Rico.)

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

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

.land {
  fill: #222;
  fill-opacity: .2;
}

.us {
  fill: #222;
}

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

.division {
  fill-opacity: .5;
  stroke-width: 2px;
  shape-rendering: crispEdges;
}

.division-label {
  font: 16px sans-serif;
  text-shadow: 0 1px 0 #fff, 0 -1px 0 #fff, -1px 0 0 #fff, 1px 0 0 #fff;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>

var width = 960,
    height = 500;

var projection = d3.geo.mercator()
    .center([0, 52])
    .scale(320)
    .precision(.1);

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

var graticule = d3.geo.graticule()
    .step([5, 5]);

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

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

d3.json("/../../data/world-50m.json", function(error, world) {
  if (error) throw error;

projection.rotate([120, 0]); // don’t rotate graticule

var y1 = projection([0, 50])[1], // if (latitude > 50°) alaska
      x2 = projection([-140, 0])[0], // else if (longitude < 140°) hawaii
      y3 = projection([0, 21])[1]; // else if (latitude < 21°) puerto rico

var division = svg.insert("g", ".graticule")
      .attr("class", "division");

// alaska
  division.append("rect")
      .attr("width", width)
      .attr("height", y1)
      .style("fill", "#aec7e8");

// hawaii
  division.append("rect")
      .attr("width", x2)
      .attr("y", y1)
      .attr("height", height - y1)
      .style("fill", "#ffbb78");

// puerto rico
  division.append("rect")
      .attr("x", x2)
      .attr("width", width - x2)
      .attr("y", y3)
      .attr("height", height - y3)
      .style("fill", "#98df8a");

division.append("line")
      .attr("x1", x2)
      .attr("x2", width)
      .attr("y1", y3)
      .attr("y2", y3)
      .style("stroke", "#2ca02c");

division.append("line")
      .attr("x1", x2)
      .attr("x2", x2)
      .attr("y1", y1)
      .attr("y2", height)
      .style("stroke", "#ff7f0e");

division.append("line")
      .attr("x2", width)
      .attr("y1", y1)
      .attr("y2", y1)
      .style("stroke", "#1f77b4");

var label = svg.append("g")
      .attr("class", "division-label");

label.append("text")
      .attr("x", 6)
      .attr("y", 6)
      .attr("dy", ".75em")
      .text("1. If latitude >50°, Alaska.");

label.append("text")
      .attr("x", 6)
      .attr("y", y1 + 6)
      .attr("dy", ".75em")
      .text("2. Else if longitude <-140°, Hawaii.");

label.append("text")
      .attr("x", x2 + 6)
      .attr("y", y3 + 6)
      .attr("dy", ".75em")
      .text("3. Else if latitude <-21°, Puerto Rico.");

label.append("text")
      .attr("x", x2 + 6)
      .attr("y", y1 + 6)
      .attr("dy", ".75em")
      .text("4. Else lower 48.");

svg.insert("path", ".graticule")
      .datum(topojson.feature(world, world.objects.land))
      .attr("class", "land")
      .attr("d", path);

svg.insert("path", ".graticule")
      .datum(topojson.feature(world, {type: "GeometryCollection", geometries: world.objects.countries.geometries.filter(function(d) { return d.id === 840 || d.id === 630; })}))
      .attr("class", "us")
      .attr("d", path);
});

function parallel(φ, λ0, λ1) {
  return d3.range(λ0, λ1, λ1 > λ0 ? 1 : -1).map(function(λ) {
    return [λ, φ];
  });
}

</script>

Changed /mbostock/raw/4090846/world-50m.json to a local referenece

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

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