Postcodes: how do they work and what can they do for us?
We all (should) use postcodes. That handy series of letters and numbers coupled with a building name or number is all that is needed to get deliveries to our door. Unlike many other postcode systems, U.K. postcodes are easy to decode and geographically descriptive. Since their widespread introduction almost 50 years ago, postcodes have been used to get deliveries to the correct address, describe areas and localities, and as an effective way to geocode and map other data.
More about postcodes:
- Postcode-to-postcode journey planning
Postcodes give us a great key around which to plan travel, but for fleet or salesforce planning the calculations can be staggering.
- The geography of government
How administrative geography has developed, how it works and how it compares to postcode geography.
- The power of postcode sectors
Grouping postcodes together into areas is a powerful geographic analysis tool but isn't as easy as you might think.
A brief history of the humble postcode:
When and why were postcodes introduced?
It all started during the reign of Queen Victoria. London’s population grew rapidly throughout the 19th century. In 1800 the population was just over 1 million, but by 1900 the population was over 6 million. The amount of post carried reflected the rise in population. In 1854 The Postmaster General, Charles Canning, set up a committee to investigate how best to divide London in order to route and distribute mail more efficiently.
The problem was not trivial, in 1856 the London population of about 3 million received 100 million items of post. The project, managed by Sir Rowland Hill, came up with a nearly circular area drawn 12 miles around the central post office near St Paul’s Cathedral. This was divided into 10 districts.
A timeline of key postcode developments:
- 1857/8: London is divided into 10 districts:
East Central (EC), West Central (WC), North (N), North East (NE), East (E), South East (SE), South (S), South West (SW), West (W) and North West (NW).
- 1864/5: Liverpool split into Northern, Eastern, Southern, and Western districts.
- 1866: London NE merged into the London E district.
- 1867/8: Manchester and Salford split into 8 numbered districts.
- 1868: London S district split between London SE and London SW.
- 1917: London postal districts split into numbered sub districts to improve efficiency.
- 1934: Numbered districts introduced into “every provincial town in the United Kingdom large enough to justify it”: Birmingham, Brighton and Hove, Bristol, Edinburgh, Glasgow, Leeds and Bradford, Liverpool, Manchester and Salford, Newcastle upon Tyne, and Sheffield.
- After 1945: Mail volumes grow. A postcode system was needed to facilitate automated sorting.
- 1959: Norwich selected to trial a postcode system as they had eight new automated sorting machines.
- Early 1960s: The Royal Mail starts a mechanisation program to introduce reliable mechanical sorting. Sorting machines needed the address to be machine-readable, so a code system was developed from the Norwich trials.
- 1965: The Postmaster General, Tony Benn MP, announced postal coding would extend to the whole of the UK over the next few years.
- 1967: New postal codes introduced in Croydon.
- 1967 - 1970: Rollout of new codes to major centres: Aberdeen, Belfast, Brighton, Bristol, Bromley, Cardiff, Coventry, Manchester, Newcastle upon Tyne, Newport, Reading, Sheffield, Southampton and the Western district of London.
- 1971: Addresses receive notification of their own postcodes.
- 1974: Coding is completed. Norwich is the last place to be re-coded.
How does the modern UK postcode system work?
So how does this collection of letters and numbers fit together to make a rational and reliable system?
Put simply, the first half of the postcode is the “outbound” code, allowing a letter to be sent to the correct part of the country; this is made up of between two and four alphanumeric characters.
The second part, the “inbound” code, is then used to pinpoint the exact neighbourhood and postal round it needs to go to; this always follows a space and has three alphanumeric characters. Let's take a look at an example:
Example: The elements of postcode YO30 5QW
- Outward code
- Area: YO: One or two alpha characters subdividing the country.
- District: 30: One or two alphanumeric characters subdividing the area.
- Inward code
- Sector: 5: One numeric character subdividing the district.
- Unit: QW: Two alpha characters showing a group of buildings, a street, part of a street or a single delivery point.
Of course each element has a lot more too it than that, so let's look at each in more detail from largest to smallest. Please keep in mind that the postcode network is constantly changing and this data is just a snapshot at the time of writing - November 2020.
1) Postcode Area
125 postcode areas cover the United Kingdom, with each varying in size and population. They are usually named as a mnemonic to identify the area or Post Town they cover. E.g. AB: Aberdeen and YO: York. Most of the names are obvious but there are some mismatches, for example Rochester in Kent has an area code of ME for Medway and Lerwick in Shetland has a code of ZE for Zetland (an archaic spelling of Shetland).
London developed a postal code system in the 19th century, so area codes in London are taken from the earlier system. E.g. N: North London, WC: West Central London.
- Smallest size WC, West Central London (1 square mile ).
- Largest size IV, Inverness (6,243 square miles).
- Average size 776 square miles.
- Smallest population ZE, Shetland (22,990 people).
- Largest population B, Birmingham (2 million people).
- Average population 548,946.
- Smallest number of districts in an area ZE, Shetland (3).
- Largest number of districts in an area BT, Belfast (80).
- Average number of districts in an area 23.
2) Postcode District
Almost 3,000 postal districts cover the UK. Postcode Districts are used to subdivide postal areas and help route mail to its sorting office.
Districts fall into areas. On average there are 23 districts in an area. The actual number varies between 3 and 77. Each one varies in size and population quite considerably.
- Smallest size is EC2N, East Central London (0.03 square miles ).
- Largest size is IV27, (1,393 square miles).
- Average size 33 square miles.
- Smallest population UB11, West Drayton (10).
- Largest population CR 0, Croydon (165,894).
- Average population 23,595.
3) Postcode Sector
The UK has about 11,200 postal sectors. Sectors are used in the inbound code to help pick the delivery round. There are between 1 and 10 sectors to make a district. On average each district has 3 sectors.
- Smallest size EC3A 1, London, (less than 0.001 square miles).
- Largest size IV27 4, Lairg, Sutherland, (1,393 square miles).
- Average size 9.7 square miles.
- Smallest population EC3V 0, London (0).
- Largest population E12 6, Little Ilford, London (26,578).
- Average population 7,001.
4) Postcode Unit
A unit postcode describes a street or part of street, a single address, a group of properties, a subsection of a property or an individual organisation or department within an organisation. There are more than 1.7 million (1,770,724 as at November 2020 ) unit postcodes. This number changes regularly as around 2,750 postcodes are created and 2,500 are terminated each month.
The allocation of postcodes depends on the amount of mail received. Large users of mail such as the DVLA have different postcodes for different departments. The unit postcodes are used to find about 30 million actual addresses or delivery points, the minimum number of delivery points for a postcode is one, the maximum is 100, and on average the postcode is allocated to 17 delivery points.
There are on average 180 postcodes to each sector: the most being 390, the least is 1. The theoretical maximum is 400 because the last two letters are not allowed to be any of C, I, K, M, O, V. That leaves 20 for each letter.
Postcodes, not just for post
Since their inception, postcodes have become more than just a tool to help address mail. As postcodes nest into sectors, districts and areas, the postcode has become a handy label to define geographical locations.
Postcode boundaries provide a convenient way to tie people into manageable groups with similar lifestyles and outlooks to form the building blocks of geodemographic analysis.
Postcode mapping and geographic analysis:
Although postcodes focus on addresses, their aggregated groupings and boundaries provide an ideal building block for geographic analysis. Most businesses have data that is attached to postcode information. This could be customer records, or sales receipts for a store where the customers are most likely to travel to. Having data attached to postcodes opens up analysis and comparisons using census or other demographic data. Our own GIS systems can use postcodes as their geographical key.
Journey and logistics planning:
Postcodes are a far more accessible reference than coordinates or longitude and latitude making them ideal for setting departure and destination points in navigation tools. However, the sheer number of postcodes means that when you move beyond individual journeys, for business or fleet logistics planning the calculations required quickly become unmanageable.
Alternatives to postcodes: the geography of government
Despite their history, postcodes are comparatively new, and the UK government had already developed its own way of dividing the country into manageable administrative areas – imaginatively called “Administrative Geography”. In existence in some form for more than 1,000 years, the divisions are based on long-standing counties and parish boundaries, which have themselves changed and been sub-divided over the centuries.
These boundaries do not correspond to postcode geography very accurately and it is not unusual for a postcode area to seem misleading when you consider the county on an address, for example; the NR postcode (Norwich) doesn’t mean that you necessarily live in the Norfolk administrative county. As such, The Office for National Statistics (ONS) produces a directory of all current and terminated UK postcodes matched against the various UK administrative geographies. This reference source ties postcodes to census and other demographic datasets.
As you can see, postcodes have developed into far more than just a means of directing your post, they have become a fundamental building block for navigation, logistics and economic operation.
Postcode mapping for business is what we do, so forgive us if we seem a little too passionate about the subject, but I'm sure you'll agree, there really is a lot to the humble postcode.
We've spent more than 25 years working with postcode geography and postcode mapping.
If you'd like to see if we can help your business, please get in touch.
online or call us on:
Our other blogs
Cycle to work day
Each year for #cycletoworkday we take a look at cycling statistics across the country and try to map that data and find interesting trends. This is mainly because we at Beacon Dodsworth are either a little bit obsessed about cycling, or we tend to worry about the environment.
Mapping for local projects
Recently, we were contacted by a company responsible for organising charity door knockers. They needed more than 9,000 postcode sectors mapped at A4 size to use at a local level to plan fundraising routes and clearly define territories for each agent.
Social change over 10 years
With the next census due to take place this year, we thought it was a good time to take stock of some of the changes and trends we noticed between the 2001 and the 2011 census. What difference does 10 years make to our society and the people that live within it?
Beacon Dodsworth New Office
Now we are back in the office, we continue to support hybrid working. So, we’ve taken the opportunity to downsize our office to make us more resilient to future lockdowns, staff self-isolation, and any other uncertainty the modern world might throw our way.
Postcode to postcode drive time and distance
What happens if we want a postcode to postcode drive time lookup table?
How to create a postcode map
Turning a list or spreadsheet of postcode data into a series of points on a map isn't as simple as using an Excel wizard to do it for you, but it isn't rocket science. We look at the best way to create a postcode point/pin map.
Administrative geography is a way of dividing the country into smaller sub-divisions or areas that correspond with the area of responsibility of local authorities and government bodies. We take a look at administrative geography, what it is and how to use it.
What is geodemographic profiling?
More than 64 million people live in the UK, each with their own outlook, priorities, needs and way of life. Geodemographic profiling offers a way to group these individuals to try and identify the right audience for your product or service.
Who spends most on Fruit and Veg
National Vegetarian Week (#NationalVegetarianWeek) this year ran from 10th to 16th May. It gave us the opportunity to highlight how GIS mapping can be used to create marketing campaigns and raise awareness of the benefits of eating more fruit and veg.
Using geographic intelligence to grow the UK’s broadband network
Using geographic intelligence to sustainably grow the UK’s broadband network.
Data visualisation and colour blindness
John, our director talks about living and working with colour blindness in the mapping industry where colours are pivotal in adding dimensions to people's understanding.
How far is it to the beach
We use Beacon Dodsworth's scripting technology to answer that most important of questions when the sun finally does threaten an appearance.
All you need to know about postcodes but were afraid to ask
The humble postcode has been around for years. We look at how postcodes are used and what led to their introduction.
TimeTravel: the latest update
We look at the latest update to TimeTravel, our dataset of drive times and distances between any postcode sector or district. What has changed in the UK road and geographic network, plus new features to make it even more accurate.
British Population Survey (BPS)
The British Population Survey (BPS) is a survey of household income and shopping habits collected by face-to-face interviews. We take a look at the BPS in detail, what exactly it is made from and how its data can be usefully applied by businesses and public organisations.
As a Yorkshire-based company, we wanted to help celebrate Yorkshire Day, which takes place on 1st August. Naturally, we wanted to put a geographic spin on the celebration, so we took a look at drinking preferences within God’s own county.
The foundations of geographical analysis
Displaying data on maps makes it easier to understand as well as giving a new perspective on a problem. Using a GIS to prepare and present data has become increasingly popular over the last 20 years, but graphical displays of data on maps were around long before computers came along.
How to back up your Prospex data
Keep your GIS projects safe by using the in-built Prospex back up process. Here is how.
The power of postcode sectors
Postcode sectors are aggregations of individual postcodes and they provide meaningful geographical reporting areas in any GIS. However, they aren't as easy to map as you might think. Here is how we do it.
Living Costs and Food Survey
The Living Costs and Food survey (LCF) is compiled every year and is used by the UK and European governments, Department for Transport (DfT), and Her Majesty’s Revenue and the Customs (HMRC). But what is it, and why should we care?
The new normal for the GIS world
Toby, our Account Manager, looks at the changes to working style and client needs in the geodata industry following the COVID-19 outbreak.
Where is the North
We've used the territory manager tool in Prospex GIS to split the UK into north, south and east and west with equal population counts.
What is GIS software?
A Geographical Information System (GIS), is a tool for analysing, visualising, managing and presenting data that is related to a physical, geographical location. That link to geography is the key difference between GIS and other data visualisation techniques.
Mapping GP prescription data
An article by Allan Brimicombe (Head of Centre for Geo-Information Studies at the University of East London) & Pat Mungroo on using GP prescription data to understand health needs.
Geodemographics and the University of East London
The University of East London explain how they have been using our P² People & Places geodemographic classification.
The census helps you to understand your customers
The UK Census 2021: what it is, how is it made, and how can it be used to help your organisation with demographic analysis.
Google Fusion Tables
After almost 10 years of service, Google retired their Fusion Tables product at the end of 2019. This tool was very useful at visualising and sharing large amounts of tabular data - particularly amongst small and mid-sized businesses. So what can we do to fill the gap left by this tool?
Your continued use of this site is taken as implied consent to receive cookies from us and our analytics partners.