title: How do you query your dataset when you zoom into and out of a d3 map?
body: <ol>
  <li>How do you add interactivity to d3 maps?  </li>
  <li>I want to add functionality to query my dataset when you zoom into and out of a d3 map. Is there a callback or something that will enable me to do this?<br>
  <em>2.1 I also want the transition to the new data displayed once you zoom to be fairly seamless.</em></li>
  </ol>