The first two digits of the ZIP Four identify an area known as a sector and the last two digits identify a smaller area known as a segment. Together, the four digits identify geographic units such as a side of a street between intersections, both sides of a street between intersections, a building, a floor or group of floors in a building, or a firm within a building. For mailing addresses, it could also identify a span of boxes on a rural route or a group of post office boxes to which a single USPS employee makes deliveries.
See also:
postal_code- Data Dictionaryzip- Data Dictionary