Postcode Unit An area covered by a particular postcode. Postcodes are an alphanumeric abbreviated form of address. Postcode units are unique references and identify an average of 15 addresses. In some cases, where an address receives a substantial amount of mail, a postcode will apply to only one address (a large-user postcode). The maximum number of addresses in a postcode is 100. A sub-area of a postcode sector, indicated by the two letters of the inward postcode, which identifies one or more small-user postcode delivery points or an individual large-user postcode. There are approximately 1.7 million postcode units in the UK. Description of http://data.ordnancesurvey.co.uk/ontology/postcode/PostcodeUnit