That in itself makes the Valuation an important historical record. But it also turns out that it can give a picture of the settlement patterns of Ireland over many centuries previous to the Valuation. The Irish seem to have done a surprisingly small amount of moving around their island over the centuries. The grown children of each generation tended to settle within a few miles of the rest of the family. Therefore in places where the Griffith Valuation shows a clustering of a surname, it often turns out that the historical accounts of the surname's origins will mention that same area. This can to hold true for some settlements/invasions going back nearly 1000 years.
A few examples are shown below in links to distribution studies on several Irish surnames in my own lineage.
There are also interesting patterns to be seen in the distribution of given names in Ireland.
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