Constrained Zoom

This example demonstrates using the zoom event to constrain the zoom behavior’s translation. This implementation is a bit heavy-handed, as the translate constraint is zoom-dependent.

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

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

.land {
  fill: #000;
}

.boundary {
  fill: none;
  stroke: #fff;
  stroke-linejoin: round;
  stroke-linecap: round;
}

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

var width = 960,
    height = 500;

var projection = d3.geo.mercator()
    .translate([0, 0])
    .scale(width / 2 / Math.PI);

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

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

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height)
  .append("g")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")")
    .call(zoom);

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

svg.append("rect")
    .attr("class", "overlay")
    .attr("x", -width / 2)
    .attr("y", -height / 2)
    .attr("width", width)
    .attr("height", height);

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

g.append("path")
      .datum(topojson.feature(world, world.objects.countries))
      .attr("class", "land")
      .attr("d", path);

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

function move() {
  var t = d3.event.translate,
      s = d3.event.scale;
  t[0] = Math.min(width / 2 * (s - 1), Math.max(width / 2 * (1 - s), t[0]));
  t[1] = Math.min(height / 2 * (s - 1) + 230 * s, Math.max(height / 2 * (1 - s) - 230 * s, t[1]));
  zoom.translate(t);
  g.style("stroke-width", 1 / s).attr("transform", "translate(" + t + ")scale(" + s + ")");
}

</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