This article presents a substantive analysis using the Great Britain Historical Geographical Information System (GIS), one of the earliest national historical GISs. It develops exploratory techniques to explore local patterns of demographic change and applies these to the study of infant mortality in England and Wales from 1851 to 1911. The techniques developed could be applied to a wide variety of fields where the aim is to explore long-term spatio-temporal change using data published for administrative units that are affected by boundary changes. The Victorian and Edwardian eras saw the origins of the sustained infant mortality decline that characterized the entire twentieth century. Although the period has been extensively studied for a century and more, our knowledge of this vital phase is still surprisingly limited. In particular, much of the research to date has focused on urban areas and has thus stressed urban explanations as to why infant mortality began to decline. Because this article uses a comprehensive GIS database, we are able to challenge some of the orthodoxies that have emerged. It reveals that patterns of infant mortality decline in different parts of the country were more complex than has previously been described. Far from the national rate being driven by changes in urban areas, the largest declines and earliest declines in infant mortality were found in rural parts of the southeast of England, as the rural periphery lagged far behind. Urban areas were slow to decline due to the specific conditions that existed in them in this period.