Historians can be reluctant to use maps - despite the availability of computer tech-niques. But in 1991, staff at Queen's University, Belfast, started converting census statistics for Ireland into machine-readable form. We decided to map the immense detail revealed in these new datasets in a bid to throw light on a key historical event - the great potato famine of the 1840s. The resulting atlas includes maps on population, diet, emigration, wages, mortality, religion, and agricultural change. Mapping the digital census data unexpectedly revealed that the famine's impactwas not always worse in the westof Ireland.