Since geographic information systems (GIS) began to emerge as an effective spatial information processing technology, there also has been growing interest in integrated use of GIS with other decision support systems. As various spatial-related problems such as urban development planning and natural resource management require more analytical and interpretive solutions, it is viewed that the supportive role of GIS to complement or reinforce the counterpart decision tools will be increased. This study examines the major situations that have needed the integration methodologies in the past decade to derive research trends relating to this integration agenda and, hence, to elicit the possible underlying principles from those experiences. According to the kinds of decision tools linked with GIS, alternative methodologies and viewpoints are categorized and compared.