The vast majority of records used for genealogy or local history are snapshots of a particular instant: a wedding, a single evening in April 1911, a newspaper announcement. In contrast, those few sources that give ongoing revisions over extended periods are like motion pictures, adding depth and nuance and offering something like a narrative.
The single most important such source is certainly the Valuation Office's vast collection of revisions to Griffith's, impassively chronicling almost 150 years of family and political upheaval through the records of the occupiers of every single property in Ireland (valoff.ie). But for Dublin and Belfast, the VO collection is rivalled by the urban street directories, Henderson's for Belfast (online at proni.gov.uk) and Thom's for Dublin, up to now best accessed in hard copy at the Gilbert Library in Pearse St.
For anyone whose family was involved in a trade or profession of any sort in Dublin, the annual alphabetical listings in Thom’s have long provided an invaluable decades-long trail into the past. Just as important is its separate street-by-street, house-by- house listing of residents, also revised annually. But these lists have never had an alphabetical key. So once a Dublin family not involved in trade moved house – and families in Dublin seem to have moved almost every other year – it was virtually impossible to find them again.
No longer. A digitised run of Thom's from 1844 to 1900, 58 full years, has recently been released on FindMyPast.ie, searchable by name and year, and (praise be) browsable back and forth from page to page. The way it's done doesn't as yet fully realise the potential of the source – not being able to search by locality and subsection (as you can at Proni) makes research a bit cumbersome. But that full name search spanning six decades is spectacular, an entire new frontier in Dublin local history and genealogy.
Hearty congratulations to FindMyPast. Keep it up. And make it better.