As data-driven decisions become ever more pervasive in our lives, the humble postcode has achieved a level of significance that goes way beyond its original vision. The story of the postcode provides some valuable lessons in data standards and all that entails…

A brief history of the postcode

Postcodes were first created by the Post Office in the 1850s and covered the central areas of London. The codes – denoting a district and sub-district – were linked to individual sorting offices and in the decades that followed the system was implemented in other major towns across the UK. The modern postcode system was implemented in the 1960s with the first codes being allocated to addresses in Norwich. The system was designed to support the use of automatic mail sorting machines and as the new coding system was rolled out across the country a major publicity campaign was launched to encourage the public to use the new postcodes on all of their mail. The majority of postcodes map directly to a physical UK location though the coding system includes things like the British Forces Post Office (BFPO) codes for service personnel posted overseas.

The postcode system also allows for personalised postcodes – the corporate equivalent of a personal number plate on a car. These are widely used by all sorts of organisations in the UK, for example HESA with the postcode GL50 1HZ.

Postcode as a data standard

Postcodes are now deeply embedded in the national psyche: research has shown that you are more likely to remember your home postcode than your wedding anniversary or your partners birthday. This widespread adoption and high public awareness enables all sorts of services to be driven by postcode data and postcode has become the de-facto standard for identifying locations in the UK.

The relationship between postcode and location underpins all kinds of geo-spatial data analysis and mapping applications like Google Maps and satnav systems in cars. It influences insurance premiums and is used by all sorts of regional services like telecoms and local authorities. Disparities between health provision in different regions has led to the phrase ‘postcode lottery’ becoming a staple of headline writers everywhere.

But UK postcodes are not designed to perform these functions and, while they often provide a link to location that is good enough, they can fail with all sorts of consequences. A few years ago a Universities Minister visited Reading University. The ministerial car arrived to collect the Minister and the driver punched the university’s postcode into the car satnav system. 90 minutes later the car arrived at a non-descript industrial estate on the outskirts of Reading and frantic phone calls ensued. It turns out that Reading University uses a PO Box address and that the university’s postcode resolves to a sorting office on the edge of town.

More seriously, the use of postcodes in socio-economic analysis is often challenged where single postcodes contain households that fall into a range of socio-economic groups. This frequently happens in areas of very dense housing – city centres and the like – and in areas of very low density housing like the Scottish Highlands where a single postcode can have a very large geographic footprint.

There are also many cases where postcodes don’t provide sufficient coverage or granularity. For example, local authorities and emergency services need a method of encoding location information for buildings and structures that do not receive mail deliveries; things like public toilets and lampposts. 

The National Land and Property Gazetteer is an initiative to create a coherent universal address infrastructure including properties that fall outside the scope of the postal delivery system. This initiative brings together Local Land and Property Gazetteers which are maintained by local authorities in England and Wales in a standard format. British Standard BS7666 defines the data structure and the work is now led by the Ordnance Survey. Agreement between the Ordnance Survey and Scotland’s Improvement Service has created a GB-wide address gazetteer.

Postcode takeaways

For me there are two key lessons from the story of the postcode. The first is the idea that standards can emerge, often unplanned, where the world has a compelling problem to solve; true standards are created by the market and not by bodies who think they have the right to impose their data specification on others.

The second key lesson for me is about the difficulties of repurposing data. Postcodes are designed to support the delivery of mail and although their adoption for other use cases can often achieve good results there are issues with scope and coverage, as well as a myriad of edge-cases and oddities, which cause problems. There are limits to the value that can be driven from repurposed data and a failure to take account of this can have real world consequences.