The Atlas Objectives also have a chance to be generated when a map is completed. If an Atlas Objective is added for a specific Master and there is still an uncompleted mission for that Master on the Atlas, then the existing one is moved to the new location.
The map tier that Atlas Objectives spawn at is loosely based on the last opened map in that league.
- Natalia_GGG (November 22, 2018). "How Atlas Objectives Work". Official Path of Exile Forums. Retrieved November 22, 2018.