German municipality key
The official key identifying a German state, district or municipality in the municipality register kept by the Federal Statistical Office.
The Amtlicher Gemeindeschluessel is the key of the Gemeindeverzeichnis maintained by Destatis. The office defines it as eight digits made of four parts: two for the Land, one for the Regierungsbezirk, two for the Kreis and three for the Gemeinde.
The length states the tier, because each level is a prefix of the next. Baden-Wuerttemberg is 08, the Alb-Donau-Kreis 08425, and Aach 08335001. A district follows from a municipal key by taking its first five digits.
Where no Regierungsbezirk is represented, the third digit is 0. This zero is a code value and must be retained. Leading zeros matter throughout: nine of the sixteen Land keys begin with one.
The key is tied to a Gebietsstand, the territorial status at a given date. Mergers retire keys and the surviving municipality usually keeps its own, so a key is only meaningful alongside the date it was published for. The twelve-digit Regionalschluessel is the same scheme with a four-digit municipal-association block inserted in the middle.