Postcode district boundaries are created and maintained by National Records of Scotland (NRS). Postcode districts are represented by the outward code (first part of a postcode). For example, if the individual postcode is EH12 7TB, then the district of that postcode is EH12. Postcodes that fall within the same district are dissolved to create postcode district boundaries.
NRS publish these boundaries twice a year as part of the Scottish Postcode Directory (SPD) which should be considered the definitive source for postcode geographies in Scotland.