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UK postcode format explained
Outward code, inward code, area, district, sector, unit. Here is how a UK postcode is actually structured.
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Two halves: outward and inward
A UK postcode has two parts separated by a space, for example SW1A 1AA. The first part is the outward code (SW1A) and the second is the inward code (1AA). Together they narrow a location down to a small group of addresses.
Breaking it down
- Area — One or two letters, e.g. SW, identifying a postcode area.
- District — The area plus a number, e.g. SW1A.
- Sector — The district plus the first inward digit, e.g. SW1A 1.
- Unit — The final two letters, identifying a small set of addresses.
Why the structure matters
Because postcodes are hierarchical, they are a powerful key for lookups, routing, and analytics. A single postcode usually maps to a handful of addresses, which is what makes postcode-driven autocomplete so efficient.