Recent advances in Web technologies have opened avenues to create socio-technical platforms that can empower citizens in urban planning processes. The rise of the GeoWeb and the popularity of Web 2.0 collaborative tools can facilitate the development of a new generation of bottom-up Public Participatory GIS (PPGIS) platforms that can incorporate user-generated content into Spatial Data Infrastructures (SDIs). New service-based delivery mechanisms can provide architectural flexibility and adaptability, and enable the public to benefit from ubiquitous information access.From an e-participation perspective, Web 2.0 social networking functions support interactive communication among various PPGIS stakeholders, e.g., citizens, planners, and decision makers. The main contribution of this article is to present a reference architecture for e-planning platforms that (1) facilitates effective e-participation by allowing multidirectional map-based communication among various land development stakeholders (e.g., planners, decision makers, citizens, etc.), and (2) enables incorporation of visualization, evaluation, and discussion capabilities to support community planning processes. To achieve this, we developed a service-oriented architecture (SOA) that exploits SDI principles and Web 2.0 technologies. The platform architecture allows heterogeneous data sources, analytical functionality and tools, and presentation frameworks to be plugged into a coherent system to provide a planning and decision support platform. We present two real-world implementations of the proposed architecture that have been developed to support community engagement in the City of Calgary, Canada.