Geographic information systems and online mapping technologies have been widely used for supporting participatory decision-making in local communities. However, limited studies have been conducted to use online maps directly as a communication tool to support community discussion. In this paper, we explore the potential of using geospatial annotation technology to facilitate map-based online discussion among various stakeholders in local communities. In particular, we developed a prototype system, GeoAnnotator, which explicitly links participants' discussion contributions with their geographic references. The features of this system are based on the conceptual understanding of map-based discussion space, which guides the generation of initial system requirements. We demonstrate the utility of such systems by a hypothetical scenario of building a Smoke-Free campus in a university community.