In this poster, we introduce a decision support system (DSS) platform (City Schema) that is designed to connect a tangible interface within a 3D modeling environment (City Form) with a simulation engine for analyzing the data of the urban, transportation, energy and water systems of the city (City Analytics) to support collaborative city planning. This DSS connects two completely independent systems into one integrated system. The first system is a physical 3D model of a city with a tangible user interface that supports interactive and collaborative activities and provides users with direct manipulation interaction and intuitive interfaces. The second system is an urban modeling design tool which is a simulation engine that has several simulation modules such as operational energy, mobility, daylight, transportation and others. The DSS we present here can be used to describe a real world problem and identify possible solutions to the modeled problem through the computation of many scenarios/alternatives so that users of the DSS can evaluate, compare and select a potential solution. Our City Schema DSS consists of: database management component, simulation modules management component, and an interactive user interface with dynamic visualization and decision scenario simulations. Human factors for supporting multi-user co-located collaboration to assist decision makers in making better decisions are examined. Design implications of different interaction modalities for decision support systems and their impact on providing intuitive and engaging user experiences are discussed.