The incode, also known as the inward code, is the second half of a full UK postcode. It consists of a single digit followed by two letters, for example '1AB' in the postcode 'SW1A 1AB'. While the outcode (the first part) identifies the post town or area, the incode provides a more precise geographical reference, narrowing the location down to a specific sector and, ultimately, a small group of addresses or a single delivery point. Understanding the incode is essential for anyone working with postal geography, from logistics planners to local researchers.
What is the Incode?
The incode is always separated from the outcode by a single space. Its format is fixed: one numeric digit followed by two alphabetic characters. For example, in 'M1 1AE', the incode is '1AE'. The digit represents the sector within the post town, and the two letters pinpoint the delivery point, which can be a street, a part of a street, a single building, or even a large organisation that receives a unique postcode. Royal Mail assigns incodes to ensure efficient sorting and delivery, and each incode typically covers around 15 to 20 addresses, though this can vary.
How the Incode Fits into the Postcode System
A full UK postcode is structured as outcode + space + incode. The outcode (e.g., 'SW1A') gives a broad area, while the incode refines it. Together they form a hierarchical system: postcode area (first letter or two), postcode district (outcode), postcode sector (outcode + first digit of incode), and postcode unit (full postcode). For instance, in 'SW1A 1AB', the sector is 'SW1A 1' and the unit is 'SW1A 1AB'. The incode is therefore the key to moving from a district to a specific group of properties. Postcodes are not strictly geographical boundaries but are designed for mail routing, yet they have become widely used for mapping and analysis.
The Role of the Incode in Geography and Delivery
In practical terms, the incode enables Royal Mail's sorting machines to direct mail to the correct delivery office and then to the correct round. The digit identifies the sector, which is a grouping of postcodes within a district, and the two letters identify the exact delivery point. For researchers, the incode provides a level of granularity that is finer than a postcode district but coarser than a full postcode. It can be used to aggregate data at the sector level, which is often more statistically robust than unit-level data while still offering meaningful local detail. Many open data sets, such as census output areas or lower layer super output areas, can be linked to postcode sectors.
Why the Incode Matters for Area Research
When researching a specific area, the incode helps to understand local patterns without being overwhelmed by individual addresses. For example, you can analyse property prices, demographic profiles, or transport links by postcode sector. The incode also appears in address validation tools and mapping applications, allowing users to zoom in from a town to a small cluster of streets. Because incodes are relatively stable over time (unlike full postcodes which can be changed or added), they offer a consistent unit for historical comparison. However, it is important to note that incodes do not correspond to administrative boundaries like wards or parishes, so cross-referencing with other geographies is often necessary.
- Example incodes: '1AA' (part of central London), '2BB' (a residential sector in Manchester), '3CC' (a rural delivery point in Cornwall).
In summary, the incode is a crucial component of the UK postcode system, bridging the gap between the broad outcode and the precise delivery point. For anyone studying a locality, it offers a manageable and meaningful geographic unit for analysis.