A hierarchy is an arrangement of category columns that is based on
parent-child relationships. The levels of a hierarchy are arranged with more general information
at the top and more specific information at the bottom.
For example, you might
create a hierarchy of date-time columns with Year as the top level,
Month as the next level, and Day as the bottom level.
Creating hierarchies enables you to add
drill-down functionality to your
visualizations. For example, if you use a date-time hierarchy, you can
drill down to the data for a specific year. Then, you can drill down to the data for a specific
month.
When you drill down a hierarchy, a set of
breadcrumb links at the top of your
visualization enables you to drill back up the hierarchy.