An area chart is really similar to a line chart, except that the area between the x axis and the line is filled in with color or shading. It represents the evolution of a numerical variable following another numerical variable. If you
want to represent this evolution for several groups in the same time, you are probably interested by stacked area chart, where every groups are displayed one of top of each other. Note that an interesting alternative is probably to use
faceting as proposed below. Like often, ggplot2 is the best tool in my opinion to realise that kind of graphic. It proposes a geom_area() that allows to draw it in one line of code.
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