The city of Lagos, Nigeria does not have postal ZIP codes, because ZIP codes are specifically used only in the United States. Rather, the Nigerian Postal Service features postal codes for different regions. Lagos has two main postal codes; 100001 for mainland Lagos and 101001 for Lagos Island.
ZIP is short for Zone Improvement Plan and was implemented in the United States in 1963 to improve mail delivery times. The ZIP code points mail from a collecting postal facility to a delivering postal facility, where it can be sorted, then delivered by postal zone.
By contrast, Nigerian mail is sorted by postal code, which differs by state, town, area and street.