10m, 50m, 110m Natural Earth by almccon

index.html

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

svg {
  background: #fff;
}

#sphere {
  fill: #000;
}

path {
  fill: none;
  stroke: #000;
  stroke-width: 1;
  stroke-linejoin: round;
  stroke-linecap: round;
  comp-op: plus;
  vector-effect: non-scaling-stroke;
}

.world-10m {
  stroke: #FF0;
}
.world-50m {
  stroke: #0FF;
}
.world-110m {
  stroke: #F0F;
}

.overlay {
  fill: none;
  pointer-events: all;
}

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

var width = 960,
    height = 560;

var projection = d3.geo.robinson()
    .translate([width / 2, height / 2])
    .scale((width - 1) / 2 / Math.PI);

var zoom = d3.behavior.zoom()
    .scaleExtent([1, 8])
    .on("zoom", zoomed);

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

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

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

svg.append("rect")
    .attr("class", "overlay")
    .attr("width", width)
    .attr("height", height);

svg
    .call(zoom)
    .call(zoom.event);

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

[
  "world-10m.json",
  "world-50m.json",
  "world-110m.json"
].forEach(function(scale) {
  d3.json(scale, function(error, world) {
    if (error) throw error;

    var inner_g = g.append("g");

    var classname = scale.split('.')[0]; // Trim '.json' from the class name

    inner_g.append("path")
        .datum(topojson.merge(world, world.objects.countries.geometries))
        .attr("class", classname)
        .attr("d", path);

    inner_g.append("path")
        .datum(topojson.mesh(world, world.objects.countries, function(a, b) { return a !== b; }))
        .attr("class", classname)
        .attr("d", path);
  });
});

function zoomed() {
  g.attr("transform", "translate(" + d3.event.translate + ")scale(" + d3.event.scale + ")");
}

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

</script>