var m = [20, 120, 20, 120],
      w = 1280 - m[1] - m[3],
      h = 800 - m[0] - m[2],
      i = 0,
      root;

      var tree = d3.layout.tree()
      .size([h, w]);

      var diagonal = d3.svg.diagonal()
      .projection(function(d) { return [d.y, d.x]; });

      var vis = d3.select("#body").append("svg:svg")
      .attr("width", w + m[1] + m[3])
      .attr("height", h + m[0] + m[2])
      .append("svg:g")
      .attr("transform", "translate(" + m[3] + "," + m[0] + ")");

      d3.json("madrid-destino.json", function(json) {
      root = json;
      root.x0 = h / 2;
      root.y0 = 0;

      function toggleAll(d) {
      if (d.children) {
      d.children.forEach(toggleAll);
      toggle(d);
      }
      }

      // Initialize the display to show a few nodes.
      root.children.forEach(toggleAll);

      update(root);
      });

      function update(source) {
      var duration = d3.event && d3.event.altKey ? 5000 : 500;

      // Compute the new tree layout.
      var nodes = tree.nodes(root).reverse();

      // Normalize for fixed-depth.
      nodes.forEach(function(d) { d.y = d.depth * 180; });

      // Update the nodes…
      var node = vis.selectAll("g.node")
      .data(nodes, function(d) { return d.id || (d.id = ++i); });

      // Enter any new nodes at the parent's previous position.
      var nodeEnter = node.enter().append("svg:g")
      .attr("class", "node")
      .attr("transform", function(d) { return "translate(" + source.y0 + "," + source.x0 + ")"; })
      .on("click", function(d) { toggle(d); update(d); });

      nodeEnter.append("svg:circle")
      .attr("r", 1e-6)
      .style("fill", function(d) { return d._children ? "lightsteelblue" : "#fff"; });

      nodeEnter.append("svg:text")
      .attr("x", function(d) { return d.children || d._children ? -10 : 10; })
      .attr("dy", ".35em")
      .attr("text-anchor", function(d) { return d.children || d._children ? "end" : "start"; })
      .text(function(d) { return d.name; })
      .style("fill-opacity", 1e-6);

      // Transition nodes to their new position.
      var nodeUpdate = node.transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + d.y + "," + d.x + ")"; });

      nodeUpdate.select("circle")
      .attr("r", 4.5)
      .style("fill", function(d) { return d._children ? "lightsteelblue" : "#fff"; });

      nodeUpdate.select("text")
      .style("fill-opacity", 1);

      // Transition exiting nodes to the parent's new position.
      var nodeExit = node.exit().transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + source.y + "," + source.x + ")"; })
      .remove();

      nodeExit.select("circle")
      .attr("r", 1e-6);

      nodeExit.select("text")
      .style("fill-opacity", 1e-6);

      // Update the links…
      var link = vis.selectAll("path.link")
      .data(tree.links(nodes), function(d) { return d.target.id; });

      // Enter any new links at the parent's previous position.
      link.enter().insert("svg:path", "g")
      .attr("class", "link")
      .attr("d", function(d) {
      var o = {x: source.x0, y: source.y0};
      return diagonal({source: o, target: o});
      })
      .transition()
      .duration(duration)
      .attr("d", diagonal);

      // Transition links to their new position.
      link.transition()
      .duration(duration)
      .attr("d", diagonal);

      // Transition exiting nodes to the parent's new position.
      link.exit().transition()
      .duration(duration)
      .attr("d", function(d) {
      var o = {x: source.x, y: source.y};
      return diagonal({source: o, target: o});
      })
      .remove();

      // Stash the old positions for transition.
      nodes.forEach(function(d) {
      d.x0 = d.x;
      d.y0 = d.y;
      });
      }

      // Toggle children.
      function toggle(d) {
      if (d.children) {
      d._children = d.children;
      d.children = null;
      } else {
      d.children = d._children;
      d._children = null;
      }
      }