Hierarchy classification:

1. top of the aat hierarchies
2. Objects Facet
3. Built Environment (hierarchy name)
4. Single Built Works (hierarchy name)
5. single built works (built environment)
6. [single built works by specific type]
7. [single built works by function]
8. communications structures

Anotations

Scope note:

Visual time signals, generally including a ball that is mounted on a tall pole or rod set up on a tower or other prominent location and that is arranged to drop suddenly at a predetermined moment, such as noontime; used, for example, by ships at anchor.