Area charts are used to represent cumulated totals using numbers or percentages (stacked area charts in this case) over time. Use the area chart for showing trends over time among related attributes. The area chart is like the plot chart except that the area below the plotted line is filled in with color to indicate volume.
When multiple attributes are included, the first attribute is plotted as a line with color fill followed by the second attribute, and so on. (the latter) proportional to them.