This chapter discusses the ‘Troubled Geographies: Two centuries of religious division in Ireland’ project. The project explored long-term change in the geographies of religion in nineteenth and twentieth century Ireland through the use of Geographical Information Systems (GIS), a form of database technology designed for use with geographical data. The chapter discusses how GIS was used to better understand the geographies of religion in Ireland and how these changed over the long-term using three different databases. Firstly, historical census data for Ireland in the nineteenth and twentieth centuries which contain data on religious identity. Second, a database of the killings during Northern Ireland’s Troubles, and third a database of membership of the Presbyterian Church which gives information on religious practice.