What is a Postcode Sector Map and What is it Used For?

A postcode sector map shows the United Kingdom divided into its approximately 11,000 postcode sectors: the geographic areas identified by a code such as SW1A 1 or EH3 6. Postcode sectors sit between districts and units in the postcode hierarchy and are the level most commonly used for sales territory mapping, direct mail targeting, and franchise area planning. A sector typically covers between 2,500 and 3,500 delivery addresses, making it large enough to be manageable but small enough to be meaningful at a local level.

What is a Postcode Sector?

The UK postcode system is organised into four levels: areas, districts, sectors, and units. For a full breakdown of how these levels relate to each other, see our guide to postcode areas, districts, sectors and units.

A postcode sector is formed by combining the full outward code with the first digit of the inward code, the part of the postcode that comes after the space.

For example, in the full postcode SW1A 1AA:

There are approximately 11,000 postcode sectors across the UK. Each one covers a defined geographic area: typically a small town, a village, or a neighbourhood within a city. Sectors in dense urban areas such as central London are geographically small but may contain a high number of addresses; rural sectors covering sparsely populated areas can cover many square miles.

What Does a Postcode Sector Map Show?

A postcode sector map draws the boundaries of every postcode sector onto a geographic base map, showing exactly where each sector begins and ends. The map will typically show:

• Sector boundary lines drawn across the underlying geography
• Sector codes (such as M1 1, M1 2, M1 3) labelled within each boundary
• An underlying road network and settlement outlines for geographic context
• Colour coding or shading to help distinguish adjacent sectors

Sector boundaries are defined by Royal Mail and the Office for National Statistics. Where possible they follow recognisable geographic features: roads, rivers, railway lines, and local authority boundaries. This makes them practical to work with and easy to communicate to colleagues or clients.

Why Postcode Sectors Are the Standard for Territory Planning

Of the four levels of the UK postcode system, sectors are the most widely used for operational business planning. There are three reasons for this.

The right size. A postcode sector typically contains 2,500 to 3,500 delivery addresses. This means a realistic field sales territory can be described using 20 to 60 sectors; a direct mail campaign can be defined by selecting a handful of sectors in the target area. Working at unit level (1.8 million individual postcodes) is far too granular for most planning purposes. Working at district or area level is too broad to be operationally useful at a local level. Sectors sit in the practical middle ground.

Clean, unambiguous boundaries. Sector boundaries are consistent, published, and recognised across the UK. Unlike informal territory descriptions such as "north of the river" or "within the M25", sector-based territories are precise and easy to document. Two franchisees, two reps, or two campaign managers can each be assigned a defined set of sectors with no overlap and no grey areas.

Wide compatibility with data tools. CRM systems, direct mail platforms, geodemographic databases, and GIS applications are built around postcode sector data. Defining territories by sector code means they integrate cleanly with existing systems and allow performance to be reported at sector level without any additional data preparation.

The Main Uses of Postcode Sector Maps

Sales Territory Planning

The most common use of postcode sector maps in a commercial context. A field sales manager mapping out territories for a team will typically assign each representative a set of postcode sectors defining their area of responsibility. Sectors provide clear, defensible boundaries with no ambiguity about which rep covers which addresses.

A sector map allows a sales manager to visualise the current territory structure across a region, check that territories are balanced in terms of address count or customer density, identify coverage gaps or overlaps, and plan new territory splits or realignments.

When territories change due to headcount changes, regional restructuring, or business growth, a sector map makes it straightforward to visualise the before and after and communicate the change clearly to the team.

Direct Mail Targeting

For direct mail campaigns, postcode sectors are the standard way to define a geographic mailing area without working through individual address files. A business running a leaflet drop, catalogue delivery, or promotional mailing can select the sectors that cover its target geography and instruct a mail fulfilment provider to deliver to all addresses within those sectors.

This approach is supported directly by Royal Mail's door-to-door delivery services, which allow campaign targeting to be specified at sector level. Advertisers can use sector-level data to estimate the number of addresses in a target area, model campaign costs, and compare reach across different delivery geographies.

Franchise Area Mapping

For franchise operations, postcode sectors offer a clean and legally defensible way to define each franchisee's exclusive territory. Rather than describing a territory by a town name or rough radius, a franchise agreement can specify the exact sector codes included, with a map showing the boundaries.

This approach removes any future ambiguity about where one franchisee's area ends and another's begins, which is particularly important when territories are adjacent in urban areas or when the business expands into new locations.

Market Analysis and Coverage Reporting

Analysts use sector maps to visualise market coverage, compare performance across geographic segments, or identify areas of untapped potential. By mapping customer or sales data against sector boundaries, businesses can see at a glance which sectors are performing strongly, which are underrepresented relative to their address count, and where the greatest opportunity for growth lies.

Postcode Sectors vs Districts: Which Level Should You Use?

The choice between mapping at sector or district level depends on the size of the area you are planning across and the level of granularity you need.

Use postcode districts when you are mapping at a regional or national level and need a manageable number of units. With around 3,000 districts across the UK, district-level analysis gives a clear picture of regional performance without the detail becoming overwhelming.

Use postcode sectors when you are planning operationally: defining territories for field teams, specifying direct mail zones, or allocating franchise areas. The finer granularity of sectors gives you the control you need to create fair, practical, and unambiguous territory boundaries.

For most territory and direct mail planning, sectors are the right choice.

Postcode Sector Maps at UK Maps

The UK Maps postcode sector map range covers all major UK regions, produced from up-to-date Ordnance Survey data under licence number AC0000848283. Maps are supplied as high-resolution 300 dpi PDF files suitable for large-format printing or on-screen use.

Browse the full range: Postcode Sector Maps

Also available: Postcode District Maps and Postcode Area Maps for broader geographic coverage.

If you need a sector map covering a specific region or a custom set of boundaries, contact us about a custom map request.

Not sure which postcode level is right for your project? Read our guide to postcode areas, districts, sectors and units for a full comparison.