How do these public entities relate to each other?

The United States has more than 90,000 Jurisdictions, including 50 States, 3,300 Counties, 15,000 Cities, 16,000 States, plus Congressional Districts, Assembly Districts, School Districts, and special districts.

Each Jurisdiction has many Agencies.
Each Agency may have one or more Governing Bodies.
The Governing Bodies are made of one or more Positions.
A Position is filled by one Person at a time, and across tenures.

Jurisdictions and their Agencies are tasked with providing Services to citizens.