Geospatial Decision Support Systems (GeoDSS) use a spatial data infrastructure and presentation medium such as GIS to promote collaborative analytic decision making. This paper describes the logical principles and application of a GeoDSS methodology employed for multistakeholder electric power transmission line routing. Layered spatial data are aggregated in ArcGIS for environmental, engineering, visibility and other criteria. A twotiered Analytic Hierarchy Process (AHP) is used to identify and weight decision criteria. A participatory Delphi approach is used to compose the hierarchy and weight its features. AHP decision weights are calculated using element values and then integrated using a global criterion of impedance. GIS scripts integrate the data layers and generate a summary impedance surface that captures engineering, cultural, social and economic values. This GeoDSS is termed Enhanced Participatory Analytic Minimum Impedance Surface (EP-AMIS). EP-AMIS permits a range of simulations to be performed including spatial sensitivity analyses to evaluate corridor routing options quantitatively and model dynamic changes. EP-AMIS mobilizes the principles of distributive justice in a GeoDSS.