title: Most underused data visualization
body: <p>Histograms and scatterplots are great methods of visualizing data and the relationship between variables, but recently I have been wondering about what visualization techniques I am missing. What do you think is the most underused type of plot?</p>
  
  <p>Answers should:</p>
  
  <ol>
  <li>Not be very commonly used in
  practice.</li>
  <li>Be understandable without a great deal
  of background discussion.</li>
  <li>Be applicable in many common situations.</li>
  <li>Include reproducible code to create
  an example (preferably in R). A linked image would be
  nice.</li>
  </ol>