Geographical information systems (GIS) software tools that support synchronous collaboration efforts among distributed decision-making participants can be very useful in many application areas, such as urban planning, engineering design, disaster and emergency response, and distant learning. However, most existing GIS tools do not provide adequate support for group interaction on decision-making and design scenarios. Early efforts on developing collaborative GIS tools have focused on collaborative geospatial information sharing and presentation in a group environment, mostly adapted to centralized client-server architecture for specific applications. This thesis presents the results of a research project, aiming at providing such GIS software tools over the Internet. Based on the analysis of two mainstream architectures used in collaborative applications: centralized architecture and replicated architecture, a hybrid architecture is selected to develop a collaborative GIS framework as the platform for prototyping the aforementioned GIS tools. The discussion focuses on synchronous collaboration where people interact with each other using the system at the same time from different places. The prototype system, called GeoLink, addresses some important design and development issues such as session management and floor control through a message sending approach.