Over the years, Irish surnames have received a good deal of careful attention, from Fr Patrick Woulfe's Sloinnte Gaedheal is Gall (1923) to Edward MacLysaght's Surnames of Ireland (1969) and most recently Seán de Bhulbh's Sloinnte na hÉireann: Irish Surnames (1997). Ulster names have been particularly well served. Robert Bell's Book of Ulster Surnames (1997) and Brian Mitchell's The Surnames of North West Ireland (2010) both dig deeper than an all-Ireland approach allows.
All of them work to a similar format: summarise received wisdom about surname etymology and meaning; give rough geographic distributions; list well-known bearers of the name. They are essentially dictionaries focused on elucidating the surnames themselves, which makes them mainly of interest to bearers of the surnames and to local historians.
But the study of surnames, in particular surname distributions, can provide much broader historical evidence, especially now that technology allows historic data to be mined and examined in novel ways. One example: it is now easy to map surname variety across Ireland in the mid-19th-century Griffith's Valuation census substitute. Simply take the number of distinct surnames listed as householders in each county and divide by the area of the county. The result is an average number of different surnames per area. (goo.gl/SLr1VJ )
Unsurprisingly, Dublin has the densest concentration of names, but the area with by far the next greatest variety is the ancient tuatha of Oriel, comprising Armagh, Louth and Monaghan. The western seaboard counties (with the exception of Sligo) have surname densities far below average, even though they were the most highly populated areas. The northeastern counties, with their mix of Scots-Irish and Gaelic-Irish, have surname variety well above average. The clear conclusion is that surname variety or density is a respectable proxy for cultural diversity.
Plenty of onomastics like this can be found at the Society for Name Studies in Britain and Ireland, snsbi.org.uk.
