title: How to add zoom-in and zoom-out buttons in dc.geoChoroplethChart
body: <p>I wanted to add zooming effect to <code>dc.geoChoroplethChart()</code>. I am able to get Zoom-in and Zoom-out behavior with wheelmouse. I achieved with the help of <a href="https://stackoverflow.com/questions/24246125/how-to-add-zoom-effect-into-dc-geochoroplethchart/24407851#24407851">this</a> example. But, how to achieve this using Zoom-in and Zoom-out buttons? I tried multiple multiple ways to do this seeing d3 examples, but ended up unsuccessful and messing the code.</p>
  
  <p>Thank you.</p>