Creating spline charts

Spline charts are similar to line charts; the only difference is that in line charts, the data points are connected by a straight line whereas in spline charts, the points are connected by curves. A line chart can easily be converted into a spline chart by changing the chart type from line to spline.

Consider the following example showing Producer Price Index (PPI) in the US from 2007 to 2012:

(function() {
  $( '#chart_container' ).highcharts({
    chart: {
      type: 'spline'
    },

    title: {
      text: 'Producer Price Index (PPI) in the US'
    },
    subtitle: {
      text: 'Source: Bureau of Labor Statistics'
    },
    xAxis: {
      type: 'datetime'
    },
    series: [{
      name: 'PPI',
      data: [
        [Date.UTC(2007, 00, 01), 172.6],
        [Date.UTC(2008, 00, 01), 189.6],
        [Date.UTC(2009, 00, 01), 172.9],
        [Date.UTC(2010, 00, 01), 184.7],
        [Date.UTC(2011, 00, 01), 201],
        [Date.UTC(2012, 00, 01), 202.2]
      ]
   ...