Displaying combined charts
Combined charts are charts that have more than one x or y axis, and may have multiple types of series (lines, bars, and areas). Sometimes, we may want to present multiple heterogeneous types of data on a single chart, usually to visualize its correlation.
In this recipe, we're going to try and visualize a mountain hike by presenting both temperature and altitude on a single chart. The altitude series will be an area chart with gradient colors reminiscent of relief maps, but the temperature series will be a line chart, which we would like to be red if above 19 degrees Celsius and blue if below that.
In order to do this, we're going to need a charting library that can handle two y axes. We're going to use the Flot charting library because it is capable of displaying charts with two or more x or y axes.
Getting ready
Like in the previous recipes, we need to download Flot from the official website at http://www.flotcharts.org/ and extract the contents to a separate folder...
