I have read in the documentation that geom_area is a special case of geom_ribbon with the y-axis starting value fixed at zero. I have been experimenting with geom_ribbon and am not seeing this. The examples and discussions generally focus on putting ribbons around a plotted line using ymin and ymax parameters.
I realize this is a very open-ended question but....
Can anyone point me to a resource or example of how I can just render a simple stacked area chart with the y-axis starting at a value other than zero using ggplot2?