Concept Mapping is a method for externalizing and reflecting knowledge about real world phenomena. In cooperative settings, concept maps can also be used to aid cooperative learning activities and the development of a common understanding about the mapping subject. This process imposes requirements on tool support that have hardly been addressed in existing concept mapping tools. We present a tabletop interface designed to meet these requirements. In an empirical study, the positive effects on the cooperative mapping process facilitated by the proposed system have been shown in comparison to a traditional, screen-based system.