Collaborative spatial decision making (CSDM) involves multiple stakeholders making strategic decisions based on spatial data. Current CSDM tools have been exploring different ways to integrate spatial data with collaboration, distribution and mobility. Notably, decision-making support has not seen the same level of attention. This paper discusses the challenges raised by the integration of decision-making models in CSDM tools. We review a large collection of decision-making models using three different views: sequential, dynamic and continuous. From this review we derive a conceptual model and a set of functional requirements necessary to integrate decision-making support in CSDM tools. The conceptual model highlights the importance of several functions in decision-making processes: representing problems, finding alternatives and making choices (sequential view); classification and communication (dynamic view); and perception, comprehension and projection (continuous view). The paper also describes a prototype developed to validate the model. The paper provides two main research contributions: a unified view of decision-making support and an innovative CSDM tool blending spatial data with decision-making support.