If your ancestors came from Derry, you’re in luck! Brian Mitchell has written another book, The Top 300 Surnames of Derry-Londonderry, with maps by Sam Mitchell.
An excellent description of Mitchell’s new book can be found at the RootsIreland blog (dated 11 April 2017): www.rootsireland.ie/category/blog/.
When I expressed curiosity about co-author Sam Mitchell, Brian explained that Sam was his father. Lots of expertise in the Mitchell family!