If I understand it correctly, you have source files partitioned by application and region in cloud storage that you want to load and would like some suggestions on the Unity Catalog structure. It will definitely depend on how you want the data to be consumed and security/access control requirements. I've added some assumptions to get you started.
1. Is there a need to view the data across regions or across apps? If unsure, I would use the smallest multiple of the group for catalog level separation. For example, I would create a catalog per application and schema per region and tables under them, assuming each region has more than one table i.e. `app_1.region_1.table_1`
2. Does access need to be controlled per region or app? - If you follow above recommendation, then you can set access control at the catalog level for each app scope or schema level for each region.
You will need to consider your specific usage requirements to help determine the catalog structure. Hope this helps.