The general idea of such a system was an evolution of earlier simple postal districts in Europe, Asia, and the US.
Reading a Saudi postal code from left to right, each sequence of digits represents a narrower geographic area.
The first digit represents a large geographic administrative region within Saudi Arabia: The second and third digits (combined) are the code for the main post office in that region.
The last two digits can indicate either an individual post office or a postal zone in that particular city or surroundings.
[2] In writing addresses in Saudi Arabia, generally the 9 digit postcodes are for home addresses, while businesses and PO Boxes will only have a 5 digit postal code.