title: Cannot read property 'objects' of undefined: d3 Choropleth
body: <p>I'm throwing the error <strong>"Cannot read property 'objects' of undefined"</strong> on the below chunk of code.  Does that mean the us.json file isn't loading?  I tested it with a console log, and it does appear to be loading properly, and there <em>is</em> an <code>objects</code> property, so what's going wrong?</p>
  
  <pre><code>queue()
  
    // Load map JSON
    .defer(d3.json, 
    'https://rawgit.com/HyperrealTech/thorn-directives/master/lib/us.json')
  
    // Load applicable data
    .defer(d3.json, data)
  
    // Call rateById for each d in data
    .await(function(d) { 
      rateById.set(d.state, +d.count); 
    })
  
    // Once finished loading, call ready function
    .await(ready);
  
    // Ready function
    function ready(error, us) {
  
      // Sum values in data to arrive at total
      var total = 0;
      for(var value in rateById) {
        if(rateById.hasOwnProperty(value)) {
          total += parseInt(rateById[value], 10);
        }
      }
  
      // Append states to svg
      svg.append('g')
        .attr('class', 'states')
        .selectAll('path')
  
        // Error here
        .data(topojson.feature(us, us.objects.states).features)
  </code></pre>