what is the purpose of a zip code
The first three digits of a ZIP code refer to a sectional center or a large city. The last two digits refer to a specific post office facility or delivery area. In ZIP+4 format, a hyphen is required to separate the first five and last four of a ZIP code. The first two of the +4 code refer to a sector or a few blocks. The last two of a +4 code refer to a specific segment or one side of a street.