The administrative code consists of six digits: the first two digits represent provinces (cities, autonomous regions); The first three digits indicate the postal area; The top four represent counties (cities); The last two digits indicate the office.

Postal code corresponds a city to a numerical code, and telephone number corresponds a specific user to a numerical code for communication.

Extended data

Most digital coding uses position representation, that is, any digital quantity can be represented by the sum of some numbers. These numerical codes have different values according to their positions in the expression. In other words, each different position has its own "rights".

Decimal data system is the most familiar digital system, but it is very difficult or even unrealistic to use decimal data system in data conversion and computer processing. Ten different circuit states are needed to represent ten digital symbols respectively. But there are many ways to make the circuit show two different states, so the binary data system has been widely used.

Digital coding of digital data refers to converting binary 0/ 1 digital data into a square wave waveform (digital signal) with certain polarity, amplitude, bit rate and jumping rules.