In the larger populated cities of the time, merchants found a way to cater to busy customers who had little time or energy to prepare food during the evening. The variation in Chinese cuisine from different regions led caterers to create a list or menu for their patrons.
ZIP Code began on July 1, 1963, as scheduled. Use of the new code was not mandatory at first for anyone, but, in 1967, the Post Office required mailers of second- and third-class bulk mail to presort by ZIP Code. Although the public and mailers alike adapted well to its use, it was not enough.
For those areas where it is difficult to determine the prevailing five-digit ZIP Code, the higher-level three-digit ZIP Code is used for the ZCTA code. Based on the January 2000 list of ZIP Codes from the USPS's Delivery Type File, the ZCTA delineation process excluded 10,068 ZIP Codes in the United States and Puerto Rico (not counting overseas military ZIP Codes).