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, 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.