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Geographical Referencing Learning Resources The National Statistics Postcode Directory (NSPD) is the latest in a long series of postcode directory products produced by the Office for National Statistics (ONS). Earlier versions of the directory have variously been known as the All Fields Postcode Directory (AFPD), Central Postcode Directory (CPD) or Postzon file. These files have been produced at least annually since 1980 and the NSPD is currently released quarterly, reflecting the continual change in the postcode and administrative geographies of the UK. The earliest files do not include Northern Ireland.
Each of these shares a common basic data structure of one record for each postcode. The following fields are common to all versions of the directories:
| Field | Contents |
| POSTCODE | The full unit postcode (e.g. "SO17 1BJ") |
| DOINTR | The date when the postcode was introduced (e.g. 198001) |
| DOTERM | The date when the postcode was terminated (e.g. 199304). This will only apply to postcodes which have been terminated and not re-used. |
| USERTYPE | The postcode user type, where 0 = small user and 1 = large user. Large user postcodes are allocated to addresses receiving more than 25 items of mail per day. |
| OSEAST | Ordnance Survey Easting (X reference). The precision of these grid references has increased with successive versions of the directories from 100m in the 1980s to 1m in current versions. |
| OSNORTH | Ordnance Survey Northing (Y reference). The precision of these grid references has increased with successive versions of the directories from 100m in the 1980s to 1m in current versions. |
| WARD | Almost all versions of the postcode directories will contain a reference to the local authority ward which contained the postcode. The quality of the assignment is much greater in more recent directories and improves significantly with versions created as part of the Grid-Link initiative between Royal Mail, Ordnance Survey and ONS. |
The earliest versions of the directories contain little more than these fields, but many additional fields have been added in successive releases. Since the 1991 census, the enumeration districts (EDs), the most detailed areas in the census output geography have been included in the file and since 2003, the 2001 census geography was also added, allowing the files to be used as the basis for a lookup between 2001 and 1991 census geographies. In the late 1990s there was a rapid increase in the number of additional fields to include numerous health authority, electoral and policy-related geographical codes and also various counts of the number of delivery points at each postcode. It is necessary to check the release notes relating to each version of the file in order to be sure what is included. There are also a range of quality indicator fields which give information (for example) on the quality of the grid reference provided. If postcodes are terminated by Royal Mail, they remain on the directory until they are reused. On reuse, the old record for that postcode will be replaced by the new record, which may relate to a different geographical location and thus be allocated to different administrative units. One consequence of the additional records and additional fields is that the more modern versions of these directories are very large files if downloaded in their totality, containing around 2.3m records (of which around 1.7m relate to postcodes currently in use). These files are not suitable for manipulation in spreadsheet software such as Excel and are best manipulated in database software such as Microsoft Access or using specialist tools such as GeoConvert.
Registered UK academic users can obtain downloads of all the versions of these files purchased for the academic community by the Economic and Social Research Council (ESRC) from the UKBORDERS service http://edina.ac.uk/ukborders and can obtain extracts and undertake matching using the more recent releases of the NSPD (from May 2006) from the GeoConvert service http://geoconvert.mimas.ac.uk/.
All users are able to order copies of the most recent files for purchase directly from the ONS website at http://www.statistics.gov.uk/ - search for NSPD. This site also contains the NSPD user guide and version notes relating to the current release, which can be inspected without login or ordering.
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