An Eircode is made up of seven characters, for example D02 X285. The first three characters are the ‘Routing Key’ which can be shared by several towns and townlands. Except for Dublin postal districts the letters are not linked to a town or city name. The second part of the Eircode is the ‘Unique Identifier’ and is four characters long. Eircodes are not sequential; if your neighbour is D02 X285 you won’t be D02 X286. This is to avoid the situation where a new building is created between two existing ones, and the code sequence would be broken, requiring all Eircodes in the area to be changed.