100% Stacked Bar Charts display the comparison of the percentage each part of the category brings to the whole category, taking the whole category as 100%. So, each of the stack components shows its relative contribution (in percents) to the entire bar and the entity as a whole.
Chart shows products’ sales ratio in four regions: Florida, Texas, Arizona and Nevada. Each region is shown in an interactive legend. You can change the chart by clicking legend items, effectively turning regions data on and off. All legend items that are turned "on" form the 100%, so each time you turn on or off an item, the percentage is being recounted. Each stack represents a product, which is quite clear from the axis labels.