height - 80
var color = d3.scale.category20();

var force = d3.layout.force()
    .charge(-900)
    .linkDistance(100)
    .size([width, height]);

var svg = d3.select("topic-graph").append("svg")
    .attr("width", width)
    .attr("height", height)
    .attr("viewBox", "0 0 " + width + " " + height )
    .attr("preserveAspectRatio", "xMidYMid meet")
    .attr("pointer-events", "all")
    .call(d3.behavior.zoom().on("zoom", redraw));

var vis = svg
    .append('svg:g');

function redraw() {
  vis.attr("tra