The graphic is a scatterplot of the longitude and latitude of Napolean's army at a series of times. For each group of soldiers, the advance and retreat were plotted separately as paths. The cities were in a separate data set and were labeled with a single command. The bottom margin on the scatterplot was extended and that blank space used to draw the temperature time series.The next version of IML Workshop (version 2.1) has a built-in DrawPath command that simplifies the production of this graphic. Specifically, it does all the work of the module PlotContinuousDataPath and so that module is not needed.
The linear transformation of the Y-axis from the latitude scale to the temperature scale was explicitly programmed. While not difficult, using this technique to draw a second plot on the first is less intuitive than creating the first plot.