It is surprisingly easy to determine the Eircode Routing Key for any address

Posted by Pat Donnelly | Jun 17, 2017

The Eircode Routing Key is the first three characters of an Eircode.  There are 139 of these in Ireland, which is five times more detailed than Counties.  How easy is it to determine the Eircode Routing Key for an address?  How much of the address needs to be matched in order to be confident?  Surprisingly, you can easily and accurately determine the Eircode Routing Key for any address just by verifying one line of the address.

Eircode Routing Key

The map below shows Eircode Routing Keys .  You can see an interactive Google Map here.  The areas don't follow any administrative boundaries  (e.g. County boundaries) they have been designed by An Post to suit their sortation requirements for post.  Their irregular shapes may ​appear unintuitive, but there is an underlying logic that will become apparent later in this blog. 
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Last line of an Address

The address line we are interested in is the last line above the County name (if any).  The examples below illustrate that this is generally a Town or a Dublin Postal District (highlighted in bold)

Example 1Example 2Example 3
4 Inns Court
Winetavern Street
Dublin 8
Chancery
Turlough
Castlebar
Co. Mayo
41 Cluainbroc
Athlone
Co. Westmeath
In Example 1 and Example 3 the Autoaddress 2.0 API will automatically match the address and return the complete Eircode, but in Example 2 Chancery is a non-unique address and we can't automatically append an Eircode.   Can we return an accurate Eircode Routing Key for the address?  Yes.  What if it was only matched to Castlebar?  Yes.  What if Example 3 just had Athlone and was missing Co. Westmeath?  Yes.  What if Example 3was Athlone, Co. Roscommon?  Yes.

How?

The Eircode address database has 266 Towns.  We included in our analysis every address that has one of these Town names as the last of their address above County (even if it isn't in the Town, see this FAQ that explains Hierarchical vs Proximity addressing). This covers 70.7% of addresses, which leaves 29.3% of addresses.  To include all addresses we expanded our definition to include townlands and villages that appear as the last line of an address above County.  This increased our "Town" list from 266 to 3,802.
Then we queried all address that have one of these 3,802 "Towns" as their last line of address above County to see if any are found in more than one Eircode Routing Key.

Results

Only 18 of the 3,802 "Towns" have addresses that are in more than one Eircode Routing Key area (listed at the bottom of this blog).  The total count of buildings affected is 91,212.  Thus we can be 95.2% confident of determining the Eircode Routing Key of any given address  by simply validating the last line of the address above County.  The biggest issue is with Cork City which is split between T12 and T23 (with a small number in T45).  These comprise 42,383 of the 91,212 buildings.  Excluding Cork City we can be 98.6% confident of the Eircode Routing Key.

This shouldn't be too surprising a result.  The Eircode Routing Keys are designed around the An Post post town delivery model which sorts post by looking at a single line of address.  Incidentally, the Athlone example address we provided in the first table is actually in Co. Roscommon, not Co. Westmeath as appeared in the address.  However all of Athlone and surrounding areas are in Eircode Routing Key N37.  You need to validate more of an address to determine the correct County than you do to determine the correct Eircode Routing Key even though there are five times more Routing Keys than Counties.

Conclusion

If the Eircode Routing Key areas suit your purpose then you can have an easy to validate solution that is five times more detailed than Counties. If you want to define your own areas for distribution, franchises, etc. then we recommend using  Small Areas which can be combined to create any desired areas.  



List of Towns in more than one Eircode Routing Key

This list comprises the 18 towns that straddle more than one Eircode Routing Key, and gives the percentage of their addresses in each of those Eircode Routing Keys.

NAME

Routing Key

Address %

Roscrea

E53

95%

Roscrea

R42

5%

Ardagh

V42

92%

Ardagh

V94

8%

Cork

T23

34%

Cork

T45

1%

Cork

T12

64%

Athy

R93

2%

Athy

R14

98%

Glanmire

T45

95%

Glanmire

T23

5%

Ballymore

N39

12%

Ballymore

N91

88%

Bunratty

V14

21%

Bunratty

V95

79%

Clifden

H71

40%

Clifden

R95

60%

Kinsealy

K36

14%

Kinsealy

K67

86%

Ballymote

F56

97%

Ballymote

F91

3%

Monkstown

A94

93%

Monkstown

A96

7%

Grange

E41

31%

Grange

E91

70%

Carrigrohane

T23

19%

Carrigrohane

T12

81%

Ballingarry

E41

69%

Ballingarry

E53

31%

Newmarket-On-Fergus

V14

11%

Newmarket-On-Fergus

V95

89%

Portrane

K36

91%

Portrane

K56

9%

Clogher

F26

65%

Clogher

F28

35%

Caherdaniel

V23

42%

Caherdaniel

V93

58%

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