Urban and transportation development largely depends on innovative information technologies for decision making support in its planning and management processes to achieve beneficial economic, social and environmental outcomes. Among these technologies, techniques and tools for collaborative visualization, manipulation, and exploration of spatial information are particularly useful. Existing Geographic Information Systems (GISs), however, lack of the capability to support collaborative spatial decision making (CSDM). This thesis presents a research effort in the development of GIS software tools that support synchronized collaborations between multiple participants via the Internet, to explore urban and transportation development scenarios for collective decision making. While the design and development focused on integrating decision making tools with commercial GIS development Toolkits (e.g., Map Objects Java Edition) using collaborative Java APIs, the approach and insights gained should be of general interest. The initial usefulness testing indicates that an Internet-based synchronous GIS can help improve decision making processes of urban corridor planning and ease participation in such decision making activities.