Understand area charts
Area charts display quantitative data graphically. The area between the x-axis and the line are colored in to help you compare different portions of the chart.
Your search needs at least one attribute and one measure to be represented as an area chart.
Stacked area charts
The stacked area chart is an area chart with an attribute in the legend, which divides the area into layers.
Stacked area charts show the relative contribution to the accumulated total of a measure over time.
Stacked area charts plot the y-axis as a percentage by default. You can also view your chart with the Y-axis set to 100%. Click on the Chart configuration icon 
and select the Y-axis measure. Under Number format, toggle Stack 100% on or off. You can also click on the attribute you are using to slice with color to find the Stack 100% option.
Your search needs at least two attributes and one measure to be represented as a stacked area chart.