These are ordnance survey maps on which valuation lot numbers are superimposed. They are used to pin point the location of an ancestor found in Griffith's Valuation. These maps are available from the Valuation Office. Contact information specifiying the county and townland or town of interest.
Current maps are known as the Discovery Series. They are available from a number of online vendors including the IGSI Bookstore. The map numbers for County Cavan are in the map shown below.