School site selection within densely populated municipalities presents a complex challenge requiring the integration of a multitude of spatial, legal and social factors. This study applies a GIS-based Multi-Criteria Decision Analysis (MCDA) using the Analytic Hierarchy Process (AHP) to identify suitable locations in the densely populated municipality of Lidingö, located in Stockholm County. Seven spatial criteria were selected based on Swedish planning law and policy and priory research papers. A pairwise comparison matrix was used to assign relative weights to each criterion. These weights were based on literature findings and interpretive assumptions based on the prominence of each criterion in the research background. To test the model's robustness, three sensitivity analyses were conducted. Furthermore, Stakeholder input was gathered from former high school students. This input was used to develop an alternative weighting scheme, enabling a comparative analysis between the literature and assumption-based analysis with a stakeholder-informed analysis. While Stakeholder input gave different criteria priority, both models yielded similar high-suitability areas, reinforcing the validity of the proposed MCDA framework. The results highlight ten potentially suitable locations. The study illustrated how criteria weights and data interpretation did influence the suitability outcomes. Significant changes in criteria, such as green area access or proximity to industrial areas did alter the suitability score, but not enough to displace the Gåshaga district as the most viable option, with one specific location in Gåshaga district emerging as the most viable site. The findings support the applicability of using an MCDA-AHP approach for identifying suitable high school locations in a Swedish urban context. However, it also highlights the importance of local data availability, expert engagement, and stakeholder input.