Urban outdoor thermal discomfort (UOTD) significantly affects human health, energy demand, and overall quality of life in cities. This study presents a novel comparative approach to investigate UOTD across 12 major Iranian cities, representing diverse climatic and geographical conditions. The findings of this approach are methodologically transferable to urban areas with similar climatic and environmental characteristics. Two analytical scenarios were conducted: intra-city evaluation to assess the spatial distribution of UOTD within each city, and inter-city comparison to examine disparities among the cities. Data sources included satellite imagery, digital surface models, land cover maps, and ground-based meteorological observations during the summer period. A spatial multi-criteria decision analysis approach was employed by integrating five influential factors, with weights assigned based on the correlation (R-2) between each factor and the UOTD index from meteorological observations, giving higher influence to factors more strongly associated with UOTD, with the resulting weights as follows: albedo (0.12), normalized difference vegetation index (NDVI, 0.09), upward long-wave radiation (ULR, 0.23), downward long-wave radiation (DLR, 0.30), and downward short-wave radiation (DSR, 0.25). The results revealed strong spatial heterogeneity: Ardabil (cold and humid), Gorgan, and Rasht (temperate and humid) exhibited the lowest levels of UOTD, with over 70 % of their urban areas classified as low-risk. In contrast, Bandar Abbas and Ahvaz (hot and humid climates), along with Zahedan and Kerman (hot and arid climates), experienced the highest levels of UOTD, with >80 % of their urban surfaces falling into high or very high-risk categories. Tehran and Mashhad showed moderate and mixed UOTD patterns. Barren lands (0.85) and built-up areas (0.84) recorded the highest UOTD index values, whereas water bodies (as low as 0.10) and tree-covered areas (as low as 0.22) registered the lowest. High building density combined with limited vegetation significantly intensifies thermal stress, while proximity to water bodies and green spaces substantially mitigates it. These findings underscore the urgent need for adaptive strategies, including the expansion of green infrastructure and climate-sensitive urban design with a focus on water resources.