This paper broadly explores the relationship between spatial data, computation, and public participation in the design process. In particular we evaluate a strategy for computing alignment alternatives for a regional trail network. The computation of trail alignment alternatives is one step in a larger, collaborative process, which relies on the input of professionals, stakeholders, and the public at multiple stages. The role of computing in an early stage of the planning process is generative, and the resulting alignments serve as subjects for more detailed conversations about trail design and development. Multiple alternatives are generated through a geospatial modeling framework based on different weightings of project criteria i. e., values. The resulting maps allow for conversations and feedback about specific material realities in the landscape and the values and goals represented by the modeling framework. We evaluate the Geographic Information Systems (GIS) modeling approach for its ability to overcome shortcomings in data completeness and consistency. The results may inform future strategies for trail corridor planning, especially for multi-jurisdictional projects at the regional scale.