Authority code
Each of the approximately 6500 registration offices in Germany has its own authority code, or BKZ for short. This forms the first four digits of the passport or identity card number. The authority codes can differ in the passport and ID card because they only contain a limited number range . After the respective number ranges have been exhausted, a new authority code is issued.
An official list is not published by the authorities, which is why various collection pages have been formed on which citizens can report their authority code together with the location.