In SAP PP, work centers can be subordinated into a hierarchy structure.
A work center can be part of several hierarchies.
A hierarchy can comprise work centers from several plants.
Hierarchies are e.g. used to aggregate capacity requirements data.
Statistical work centers are used to aggregate information.
Production work centers are used for fulfilling plans and production orders, and they contain all the data required for costing, scheduling, etc.
Hierarchies can be created in TC CR21.
Hierarchies can be modified in TC CR22.