Although the concept of spatial decision support systems (SDSS) has been around for approximately 40 years, it was not until the early 1990s that SDSS found a wider recognition in geography and geographic information science (GIScience). The development of SDSS has been associated with the need to expand geographic information system (GIS) capabilities for tackling complex spatial decision problems. Over the past two decades, the SDSS concept has evolved into a field of research, development, and practice that is made up of many different approaches and frameworks, among which are Collaborative SDSS (CSDSS), Group SDSS (GSDSS), Intelligent SDSS (ISDSS), Participatory GIS (PGIS), Public Participation GIS (PPGIS), Spatial Knowledge-Based Systems (SKBS), Spatial Multi-Agent Systems (SMAS), and Spatial Planning Support Systems (SPSS). A broader perspective suggests that ...