In Tableau, a hierarchy is a structure that organizes data into levels or layers. Hierarchies are used to represent data that has a parent-child relationship, such as a geographic hierarchy or an organizational hierarchy.

For example, suppose you have a hierarchy that represents a geographic region, with the levels “Continent,” “Country,” and “City.” In this hierarchy, each continent has multiple countries, and each country has multiple cities.

Hierarchies are created by dragging and dropping fields onto the hierarchy shelf in Tableau, and can be used to create drill-down or drill-up actions in a visualization. For example, you might use a hierarchy to allow the viewer to drill down from the continent level to the country level, or to drill up from the city level to the country level.

Hierarchies are a useful way to organize and analyze data in Tableau, as they allow you to represent complex data structures and relationships in a clear and intuitive way.

I hope this helps to give you an understanding of hierarchies in Tableau!