London postcodes map. A full postcode is known as a " postcode unit" designates an area with a number of addresses a single major delivery point. Click on the links to view all the postcodes in that postcode district with their Ordnance Survey coordinates longitude latitude. They are alphanumeric were adopted nationally between 11 October 19 having been devised by the General Post Office ( ). Postal codes used in the United Kingdom are known as postcodes ( originally postal codes).