Carlo Prévil Group of Interdisciplinary Studies in Geography and Regional Planning (GEIGER), Departement of Geography, University of Quebec at Montreal, P.O. Box 8888, succ. Centre-Ville, Montréal, Qc, H3C 3P8. previl.carlo@uqam.ca Marius Thériault Department of Planning, Center for Research in Planning and Development (CRAD), Laval University, Québec, Qc, G1K 7P4. Marius.Theriault@crad.ulaval.ca Joël Rouffignat Department of Geography, Laval University, Québec, Qc, G1K 7P4. Joel.Rouffignat@ggr.ulaval.ca Combining Multicriteria Analysis and GIS to help decision making processes in Portneuf County (Québec, Canada) ABSTRACT The planning of a linear section of a park of less than 15 km generated a very complex situation in Portneuf County (Quebec, Canada). Faced with dissatisfaction from various civic groups, the county's board tried to calm down the spirits by defining a five-part scenario based on alternatives proposed by different interest groups in the debate. Since the consultations did not yield any success, the protagonists had to take the issue to the courts. In this research, we endeavour to demonstrate how a well balanced methodological approach – combining a reference frame for land conservation, geographical information systems (GIS), and multicriteria decision analysis (MCDA) - could help the territorial actors discuss their preferences, facilitate negotiations, and simplify the decision-making process. Key words: Urban and regional planning, environmental studies, geographical information systems (GIS), multicriteria decision analysis (MCDA), planning process, community participation. INTRODUCTION Urban and regional planning revets certain political dimensions, because it a priori addresses issues of social justice and it aims at dialogue. Regional planning often entails building and evaluating intervention scenarios that take into account multiple possible uses of resources, often in a context of incertitude (Fisher and Nijkamp, 1993; Hickey and Jankowski, 1997). Information related to the state and to the dynamics of territorial systems, for instance the regions, is multi-varied (including scales, time, dependences, values, beliefs and objectives), in addition to targeting a great diversity of interested parties (Previl, 2000). To be relevant,