Bump charts plot the rank position rather than the actual value.
For example, if you sell a product in a marketplace with 10 other competitors, you may want to see how the rank position of your product and the competition change over time to see if you are gaining or losing market position. You must have more than one series so that the rankings can be compared. Usually you will want dates on the category axis so the trends are shown across time.
Bump charts are only available on small multiples based on cube data.
