Postcode Area vs District vs Sector: What's the Difference?

The UK postcode system is divided into four hierarchical levels: areas, districts, sectors, and units. Each level covers a different geographic scale; from large regions covering hundreds of square miles, down to individual streets or parts of a street. Understanding the difference matters because each level serves a different purpose, and choosing the wrong one for your mapping project can lead to territories that are too broad, too narrow, or simply impractical to work with.

Here is a quick summary before we go into detail:

What is a Postcode Area?

A postcode area is the broadest level of the UK postcode system. It is identified by the one or two letters at the start of a postcode the area code. For example, SW covers parts of South West London, EH covers Edinburgh, and M covers Manchester.

There are 124 postcode areas across the UK. Each one is centred on a major town or city that originally served as the postal hub for that region. The areas vary enormously in geographic size: rural areas like IV (Inverness) or TD (Galashiels in the Scottish Borders) cover vast swathes of land, while dense urban areas like EC (Central London) cover just a few square miles.

At this scale, postcode areas are most useful for high-level national analysis comparing performance across broad regions, or building a top-level view of market coverage across the UK.

What is a Postcode District?

A postcode district adds the first number (or numbers) to the area code: SW1, EH3, M60, and so on. This is also called the outward code and it is the part of the postcode used by Royal Mail to route mail to the correct delivery office.

There are approximately 3,000 postcode districts in the UK. Districts are smaller and more precise than areas, but still cover a meaningful geographic footprint, typically a town, a borough, or a sizeable chunk of a city.

Postcode districts are a practical level for regional analysis: comparing sales performance across different parts of a city, mapping franchise territories in a mid-sized town, or segmenting a direct mail campaign at a level that is manageable to review on a map.

What is a Postcode Sector?

A postcode sector is formed by combining the full outward code with the first digit of the inward code, the part after the space. For example, in the postcode SW1A 1AA, the sector is SW1A 1.

There are approximately 11,000 postcode sectors in the UK. This is the level most commonly used for business mapping and territory planning. Sectors are small enough to be meaningful at a local level, each one typically contains a few thousand households, but large enough that a realistic sales territory can be described using a manageable number of them.

Postcode sectors are the standard unit for:

• Sales territory definition: a field sales territory might cover 20 to 60 sectors, giving a clear and defensible geographic boundary
• Direct mail targeting: campaign selection by sector allows accurate targeting without the complexity of individual address data
• Franchise area mapping: sectors offer a clean, logical way to carve up a market so that no two franchisees overlap

If you are planning any kind of UK geographic territory and are not sure which level to use, start with sectors.

What is a Postcode Unit?

A postcode unit is the full postcode: SW1A 1AA. This is the most granular level of the postcode system, and each unit typically covers between 15 and 100 delivery addresses usually a short stretch of a single street, one side of a street, or a single large building.

There are approximately 1.8 million active postcode units in the UK, with more being added regularly as new developments are built.

Postcode units are used when address-level precision is required: geocoding customer data, verifying delivery coverage, or routing field operatives to specific addresses. For mapping purposes, a full postcode unit boundary map is an extremely detailed dataset useful for specialist GIS applications, but often more granular than most business mapping projects require.

Which Level is Right for Your Project?

The answer depends on the scale of the area you are mapping and the purpose of the map.

Use postcode areas when you need a simple, high-level view of the UK; for example, a national coverage map showing which regions your business operates in.

Use postcode districts for regional analysis and comparison; comparing performance across the different parts of a large city, or mapping market presence across a county or group of counties.

Use postcode sectors for operational territory planning; defining sales territories, franchise areas, direct mail catchment zones, or delivery radius boundaries. This is the most commonly used level for business mapping and the one most UK mapping tools are built around.

Use postcode units when you need to work with individual address data; for route planning, geocoding, or delivery logistics.

Why the Boundaries Matter as Much as the Level

Knowing the correct level to use is only half the job. The other half is having accurate, up-to-date boundary data, a map that shows precisely where each area, district, or sector begins and ends, drawn to the correct geographic boundaries.

Postcode boundaries are not fixed forever. Royal Mail and the ONS update the postcode system regularly: new postcodes are created as new developments are built, and old ones are retired. A boundary map that was accurate two years ago may not reflect current boundaries today.

At UK Maps, all postcode boundary maps are produced using the latest official Ordnance Survey data, updated to reflect current postcode boundaries. Maps are supplied as high-resolution 300 dpi PDF files, suitable for on-screen use and large-format printing.

Explore UK Postcode Maps

If you need a postcode map for territory planning, direct mail analysis, or business mapping, browse our full range of postcode boundary maps:

• Postcode Area Maps - full UK coverage at area level
• Postcode District Maps - detailed district-level maps for your region
• Postcode Sector Maps - the standard choice for sales territory and direct mail planning

All maps are available as instant digital downloads. As an authorised Ordnance Survey Licensed Partner (license number 100048957), every map we supply is based on official, up-to-date OS data.

Looking for a custom postcode map covering a specific area or set of boundaries? Contact us about a custom map enquiry.