Computer-assisted concept map building from provided pieces by using Kit-build is an activity which can promote comprehension and retention. However, users are burdened with searching for pieces and organizing the layout, which are believed to increase the overall cognitive load of the activity. In this paper, we describe the Airmap interface, which uses automatic layout management and spatial separation to improve cognitive load during concept map building. Two experiments were done in which participants (N=60, N=50) built a map after reading a text. Results show that Airmap is successful in reducing cognitive load without significant differences in immediate reading comprehension. However, there is a significant difference in performance after a two week retention period. Results give new insight into the retention enhancing aspects of building closed concept maps, indicating that the cognitive load reduced by the new interface is of the germane type, affecting how deep in memory users commit the information.