This part introduction presents an overview of the key concepts discussed in the subsequent chapters. The part presents the relationship between the railroad and population distribution. It outlines the importance of connecting not only disparate demographic datasets to spatial representations of the urban fabric but also to connect scholars who will ask new and fresh questions of past populations. The part explores the European migration to America by harnessing the some 800 million names in the Family Search genealogical dataset in concert with the spatial analytical tools of historical geographic information systems. It also outlines the important role that historical geographers and historical geographic information systems scholars can play on interdisciplinary teams providing expertise in standardizing areal units, geocoding, linking historic datasets, and providing important historical context to data and the interpretation of results. It interrogates the relationship between population dynamics, economic activity, and the labour force from the 1970s to 2012.