GeoTUI is a system designed for geophysicists that provides props as tangible user interface on a tabletop vision-projection system for the selection of cutting planes on a geographical map of a subsoil model. Our GeoTUI system allows the geophysicists to manipulate in the same action and perception space since the movement of the physical artifacts is done on the tabletop and thus constrained to two dimensions. Consequently, it combines the advantages of the spontaneous conditions of user interaction that the geophysicists are commonly used to in their classical paper/pen/ruler environment with the advantages of the use of powerful geological simulation software. We conducted an extensive user study in the workplace of the geophysicists that clearly revealed that using a tangible interaction performs better than using the standard mouse/keyboard GUI for the cutting line selection task on a geographical subsoil map. Consequently, it increases the efficiency for the real-world trade task of hypothesis validation on a subsoil model. Moreover, this geological user case is complex enough to confirm the hypothesis that in space-multiplex conditions, specialized devices perform better than generic ones.