Zoom to Bounding Box by mbostock

This example demonstrates how to compute a suitable translate and scale to zoom to the bounding box of a particular feature. Click on any state to zoom in; click on the focused state or the background to zoom out.

This variant uses transform transitions to change the viewport. A slightly better approach, and one that can also allow free panning and zooming with the mouse if desired, is to use zoom transitions.

index.html

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

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

.feature {
  fill: #ccc;
  cursor: pointer;
}

.feature.active {
  fill: orange;
}

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

</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,
    active = d3.select(null);

var projection = d3.geo.albersUsa()
    .scale(1000)
    .translate([width / 2, height / 2]);

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

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

svg.append("rect")
    .attr("class", "background")
    .attr("width", width)
    .attr("height", height)
    .on("click", reset);

var g = svg.append("g")
    .style("stroke-width", "1.5px");

d3.json("/mbostock/raw/4090846/us.json", function(error, us) {
  if (error) throw error;

  g.selectAll("path")
      .data(topojson.feature(us, us.objects.states).features)
    .enter().append("path")
      .attr("d", path)
      .attr("class", "feature")
      .on("click", clicked);

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

function clicked(d) {
  if (active.node() === this) return reset();
  active.classed("active", false);
  active = d3.select(this).classed("active", true);

  var bounds = path.bounds(d),
      dx = bounds[1][0] - bounds[0][0],
      dy = bounds[1][1] - bounds[0][1],
      x = (bounds[0][0] + bounds[1][0]) / 2,
      y = (bounds[0][1] + bounds[1][1]) / 2,
      scale = .9 / Math.max(dx / width, dy / height),
      translate = [width / 2 - scale * x, height / 2 - scale * y];

  g.transition()
      .duration(750)
      .style("stroke-width", 1.5 / scale + "px")
      .attr("transform", "translate(" + translate + ")scale(" + scale + ")");
}

function reset() {
  active.classed("active", false);
  active = d3.select(null);

  g.transition()
      .duration(750)
      .style("stroke-width", "1.5px")
      .attr("transform", "");
}

</script>

Zoom to Bounding Box

Updated Example →

index.html