You can group the activity nodes and edges in an activity diagram using partitions, so that each partition models a part of the activity.
Creating partitions in activity diagrams
You can use partitions to group the behaviors in an activity diagram.Changing the alignment of partitions in activity diagrams
You can align the partitions vertically or horizontally in activity diagrams. By default, the partitions are aligned vertically.
Parent topic: Modeling user workflow by using activity diagrams
Related concepts
Activity diagrams
Canonical behavior in modeling diagrams
Constraints