This article describes a new approach for analyzing data within national historical geographic information system databases that can be used to explore long-term trends in landscape evolution. The methodology is based on clustering together areas with similar demographic characteristics to define urban agglomerations whose territorial extents and populations vary over time. The resulting database can be used in a wide range of ways that allow the empirical study of urban growth and urban sprawl. The article is based on data for England and Wales but given the increasing availability of national historical geographic information system databases for countries around the world, the approach could be replicated for a wide range of different places.