Area Charts / Stacked area
By default, the MVC Area Chart renders its series on top of one another. You have the ability to stack them atop one another instead, so that the data values at each x-value are summed. In an area chart, the value for each series will always be stacked relative to the preceding one.
You can enable the stack feature through the SeriesDefaults -> Area -> Stack(true) setting.
For more information inspect the SeriesDefaults option in the documentation.