title: Multiple target lines in Google Visualization
body: <p>I'm using Google Visualization to display a target vs performance chart. The chart is split into a few months, and within each month, I have several departments, each with their own targets. The actual performance will be displayed using bar (column) charts, while I'm intending to have the targets displayed as a line. For now, I've chosen to use a stepped area chart with 0 opacity and disconnected lines for the targets, as recommended by <a href="https://stackoverflow.com/questions/13178030/how-to-add-target-line-in-google-column-chart#comment19184389_13736287">this</a> comment.</p>
  
  <p>The issue now is that the stepped area chart displays across the entire category, but I need it to display only across a single column. Currently what I have is (copy and paste the code in the Google Code Playground to see the results):</p>
  
  <pre class="lang-js prettyprint-override"><code>function drawVisualization() {
    // Create and populate the data table.
    var data = google.visualization.arrayToDataTable([
      ['Month', 'Bolivia', 'Ecuador', 'Madagascar', 'Papua New Guinea', 'Rwanda', 'Average'],
      ['2004/05',  165,      938,         522,             998,           450,      614.6],
      ['2005/06',  135,      1120,        599,             1268,          288,      682],
      ['2006/07',  157,      1167,        587,             807,           397,      623],
      ['2007/08',  139,      1110,        615,             968,           215,      609.4],
      ['2008/09',  136,      691,         629,             1026,          366,      569.6]
   ]);
  
    // Create and draw the visualization.
    var ac = new google.visualization.ComboChart(document.getElementById('visualization'));
    ac.draw(data, {
      title : 'Monthly Coffee Production by Country',
      width: 600,
      height: 400,
      vAxis: {title: "Cups"},
      hAxis: {title: "Month"},
      seriesType: "bars",
      connectSteps: false, 
      series: {3: {type: "steppedArea", areaOpacity: 0}}
    });
  }
  </code></pre>
  
  <p>​
  I'm also open to other possible ideas of how to display a target vs performance chart, so other solutions that can also create such a chart would be greatly appreciated. Thanks.</p>