We describe a prototype software system for investigating novel human-computer interaction techniques for 3-D geospatial data. This system, M4-Geo (Multi-Modal Mesh Manipulation of Geospatial data), aims to provide a more intuitive interface for directly manipulating 3-D surface data, such as digital terrain models (DTM). The M4-Geo system takes place within a 3-D environment and uses a Phantom haptic force feedback device to enhance 3-D computer graphics with touch-based interactions. The Phantom uses a 3-D force feedback stylus, which acts as a virtual “finger tip” that allows the user to feel the shape (morphology) of the terrain’s surface in great detail. In addition, it acts as a touch sensitive tool for different GIS tasks, such as digitizing (draping) of lines and polygons directly onto a 3-D surface and directly deforming surfaces (by pushing or pulling the stylus in or out). The user may adjust the properties of the surface deformation (e.g., soft or hard) locally by pa...