This paper describes the results of using digital mapping techniques (Geographic Information Systems - GIS) to facilitate the translation of historical legislative documents into large-scale (townland level) maps of the Gaeltacht. The boundaries of the Gaeltacht, within the error limits of the digital spatial data, indicate the changing spatial extent of the Gaeltacht from its inception through phases of legislative reform throughout the 20th century. This spatial definition of the Gaeltacht has largely been the basis of protection for the Irish language since independence. Changes in the defining criteria and modification of areas comprising the Gaeltacht have resulted in a discontinuous modern Gaeltacht which lacks definition in any single legislative document. A digital version of the modem Gaeltacht boundary in a GIS readable format will allow its integration with other spatial datasets and gives the administrative region new clarity of definition. This paper does discuss the actual use of Irish in the Gaeltacht.