What’s in a postcode?

Much was made of the political wrangling, the failed procurement process or the amount of time it took for Ireland to finally get a postcode system.

But what makes a good postcode? We will explore current implementations, previous recommendations, and privacy implications.

Postcode 101

Designing a new National postcode system is no small endeavour. Data requires frameworks, and many aspects have to be considered.

But Eircode is not a postcode. Not in the traditional sense of a postal address. And this was specified right from the start:

“It will not require change to the current postal addresses and addresses shall not need to be numbered or streets named where currently this is not the case” (link)

Eircode is a unique identifier in a non-sequential format.

Sequential vs non-sequential

Non-sequential means there’s no relation between your code and your neighbour’s. Yours could be A65 F4E2 but nobody in your street or building will get an iteration of that unique identifier, such as F4E3 or F5E3. It will be completely random.

This has many implications. As a user, it will be hard to remember or relate to another area within your neighbourhood. As a parcel delivery company or sorting office, it means you need to rely on a machine for each and every letter. You cannot possibly commit an area or sub-area to memory. It has further implications yet for emergency services, but more on that later.

“An unstructured code however is just a series of sequential numbers and it is necessary to have a directory (either printed or electronic) to establish the precise address / location to which the address relates.” (link)

As for the routing keys, they each cover a 200 sq miles radius. Although initially pointing to a geographic area, they do not:

“The routing key will be used to help sort mail, however it is not directly linked to counties, towns and geographic features.” (link)

Further to this, you might have expected the 139 routing keys to mirror the counties they were assigned to, e.g. Cork C01, Cashel C02 or Limerick L01, Laois L45 etc. But this is only the case for Dublin. Cork is T12/T23, Cashel is E25, Limerick is V94…


A checksum is a calculation built into the code to provide error checking.
It is a check digit appended at the end, nothing you have to do or learn. Machines use it to differentiate L and 1 for example, or 5 and S. When you have millions of letters and parcels routing through your delivery system, and with human errors being made on labels, you might want this system in place.

But Eircode does not have any error-checking mechanism. This is very poor by any standard, especially if you design a system from scratch, but once again it could have serious implications:

Miscommunication of an Eircode cannot be trapped and cannot be checked by reference to a local district. A variation in the last character could send an ambulance to the other end of the county. One might rather the ambulance accidentally arrived next-door and at least was in shouting distance. (link)

Data Privacy

There are serious drawbacks from the uniqueness of its design. Each household will be assigned a unique identifier and there is no granularity. You either provide your exact location or none at all, since the code does not scale up or down. And this constitutes personal data.

For the non-initiated, Eircode might look innocuous enough, but anonymisation does not simply entail removing names or other unique identifiers.

As discussed in his journal article ‘Broken Promises of Privacy: Responding to the Surprising Failure of Anonymization’, Paul Ohm outlines how people described in anonymised datasets can be easily reidentified or deanonymised (Ohm, 2010). For example, Ohm describes Latanya Sweeney’s study on ‘Uniqueness of Simple Demographics in the U.S. Population’, which shows that a combination of ZIP code, birth date (including year) and sex can uniquely identify 87 percent of the American population.” (Open Data Ireland: Best practice handbook, Insight Centre for Data Analytics, p.63)

The Data Protection Commissioner warned the Working Group on Postcodes in 2006 that

“a public database of one-to-one postcodes would, in my opinion, give rise to serious privacy/data protection issues. Such issues should not arise in relation to a public database of area postcodes (with geo-location coordinates) typically covering 20–50 individual but unspecified addresses.” (The Postcodes Report, 2010)

And in his Twenty-Fifth Annual Report 2013, expressed a serious concern that a public database linking a code to a single unit residential address could be considered as being personal data of the occupants of that dwelling

In essence the unique seven character postcode goes beyond what an “address” is because, through the use of modern technology and “Big Data”, it can be easily assimilated into any sort of electronic device or dataset which could in turn be used for any purpose, ranging from State services to commercial exploitation. In this regard, we expressed the concern that such datasets which would be verified by this postcode could have the potential for the ready identification of sensitive information about individuals, examples of which would be to identify specific localities that have patterns of crime or illness

Yet as soon as the system went live, Eircode’s lookup system on its website disclosed that information outright.

Add to that that any lookup that you will perform online on a retailer’s website will disclose your exact address. Retailers and marketers can track you. And given the players involved, this should be very worrying indeed.

Open Data

Currently no Irish Address data is available as Open Data, i.e. freely available under an Open License.

“There is a lot of criticism from Open Data advocates that postcodes will not be made freely available and that this is a missed opportunity for widespread economic benefit” (Open Data Ireland: Best practice handbook, Insight Centre for Data Analytics, p.60)

Eircode chose a closed, proprietary model. You have to pay for access and usage:

21st Century data systems

Opening Data has strong socio-economic benefits. Denmark, having a similar population to Ireland, made its official Address Data freely available in 2002, and quantified the benefits at €30m per year from 2015.

It has implications on a wide range of topics, and considerations must be made on many levels, such as privacy, licensing, re-use, access…

But by keeping it proprietary, there is no benefit to society. And not only will there be no benefit to the economy, it is actually hurting it:

The Freight Transport Association of Ireland estimates that the introduction of Eircode will cost €80m to its industry, even if just 5% of small and medium businesses adopt Eircode. Its estimate is based on the assumption that any business that adopts the post code will need to pay up to 5,000 for an Eircode database on top of the cost of updating its own customer, accounts payable and accounts received databases to ensure it is compatible with the new system.
(Irish Examiner)

This would put the cost associated with adoption at €1.6 billion at 100% integration.

Who will it benefit?

  • SMEs and businesses need to purchase access and usage, and update their own systems for existing customer information.
  • The Freight association indicated none of its 200 members will use it.
  • The Emergency Services’ representatives said it could cost lives.
  • It fails citizen on data privacy issues.

The only stakeholders set to benefit are the consortium’s members.

So what’s in a postcode?

In Eircode’s case: nothing. You could not design a system and make it worse.
As for the Irish Government, the closest definition is systemic failure.