BT Technology Journal  Vol 22 No 4  October 2004 287 Bringing clay and sand into digital design — continuous tangible user interfaces H Ishii, C Ratti, B Piper, Y Wang, A Biderman and E Ben-Joseph Tangible user interfaces (TUIs) provide physical form to digital information and computation, facilitating the direct manipulation of bits. Our goal in TUI development is to empower collaboration, learning, and decision-making by using digital technology and at the same time taking advantage of human abilities to grasp and manipulate physical objects and materials. This paper presents a new generation of TUIs that enable dynamic sculpting and computational analysis using digitally augmented continuous physical materials. These new types of TUI, which we have termed ‘Continuous TUIs’, offer rapid form giving in combination with computational feedback. Two experimental systems and their applications in the domain of landscape architecture are discussed here, namely ‘Illuminating Clay’ and ‘SandScape’. Our results suggest that by exploiting the physical properties of continuous soft materials such as clay and sand, it is possible to bridge the division between physical and digital forms and potentially to revolutionise the current design process. 1. Introduction Despite the increasing availability of sophisticated forms of digital representation and analysis, many designers still value the use of physical models in the planning and design process. Contemporary architect Frank O Gehry, for instance, often uses physical models (which are later digitised) in the early stages of design explorations. Automobile designers work extensively with physical, tape and clay models, even if they have access to sophisticated curved-surface modellers. On the one hand, there is great efficiency in representing physical structures with physical, tangible media, since they only differ in scale and/or material from the final outcomes. Physical models offer the user an intuitive understanding of complex geometries and physical relationships that are difficult or indeed impossible to describe with pixels on a flat computer screen. They better support rapid ideation and form giving (dynamic sculpting), especially in the initial (upstream) phase of design. Also, they support collocated collaboration better than most existing computational media. On the other hand, computer-based models, while commonly being limited to 2-dimensional visual representations, offer many advantages over physical models. The dynamic qualities of the screen allow computational systems to represent entities or forces that change over time. They offer a vast increase in the efficiency of production, reproduction and distribution via the Internet. They also offer the ability to work directly with numeric data and at accuracies that far surpass the tolerances of most physical models. In general, they are more suitable for the final (downstream) phases of design where greater precision and quantitative analysis are required. As a result, a fracture appears in most creative processes — a disjunction between physical and digital forms of representation and analysis, especially between the upstream of exploratory design and the downstream of analytical design. This paper presents two tangible user interfaces (TUIs), namely Illuminating Clay and SandScape, that aim to bridge this fracture by creating a seamless interface between physical and digital design in the field of landscape architecture. TUIs give physical form to digital information and computation, facilitating direct manipulation of representations. Our hypothesis is that utilising our physical abilities of grasping and manipulating materials can advance the design process, enable deeper learning, and increase collaboration among designers and technologists [1]. Until recently, most TUIs, such as ‘Urp’ (urban planning workbench [2]), were designed to address the relatively structured downstream aspect (final phases) of the design process based on discrete object-oriented representations allowing rich representations of semantics and the reconfiguration of spatial relationships among discrete objects. However, such a discrete object-oriented approach has a serious limitation in that it does not support the form giving that is critical in the initial (upstream) phases of the design process. In order to go beyond this limitation and support rapid sculpting with real-time computational analysis, this paper presents new forms of TUIs, which we have termed ‘Continuous TUIs’.