Community Identification Number
The municipality key has eight digits, which are set like this: The first two numbers tell people what the German state is.  The third number say the government district (in areas without government districts a zero is used instead).  The fourth and fifth numbers show people the number of the urban area (in a city without districts) or the district (in a city with districts).  The sixth, seventh, and eighth numbers show the municipality or the number of the municipality-free area.