This paper presents a generic visual tool for mapping and analyzing the evolution of a system of cities on a long-term period (2 centuries), in France and United States. The project started in 2008 in the framework of an a national grant (Action Nationale de la Recherche Corpus et Outils de la Recherche en SHS Harmonie-cités : construction de bases de données harmonisées sur les populations, les activités et les réseaux des villes). The conception of a visual tool for exploring the database represents the last part of this project and has been developed recently. Three main objectives were challenged: Designing a generic tool, that could be possibly used in the future for several countries under study, allowing a dynamic exploration of the different databases, which raises a range of difficulties as they are spatio-temporal and multi-level (cities themselves and systems of cities), giving an interactive application, that could be used by a large range of Internet users, from pupils to researchers or urban planners. The resulting interface combines time, location and attributes (population, area). The application integrates interactivity in order to propose an exploratory and animated cartography of urban dynamics, according to an evolutive conception of the urban system. It enables a large variety of possibilities for exploring city trajectories.