Morphological Differences in Iranian Historic Urban Fabrics Across Two Contrasting Climates Using EAC Indices: The Cases of Yazd and Amol

This study investigates the role of climate in shaping morphological differences between historic urban fabrics by comparatively examining two Iranian cities with contrasting climates: hyper-arid Yazd and humid Amol. The innovation of the research lies in the use of the Equal-Area Circle (EAC) and the calculation of a set of size-independent n-indices for historic blocks in order to enable fair comparison. After topological cleaning of the polygon layer of blocks, the indices were computed on a 100 × 100 m grid using interior/boundary sampling. To test between-city differences, the non-parametric Mann–Whitney U test was employed, together with effect size reporting (Cliff’s δ / r) and multiple-testing control via the Benjamini–Hochberg false discovery rate (FDR) procedure. The findings show that differences arise mainly in the measures of depth and compactness: nDepth in Yazd is significantly higher (mean 0.632 vs. 0.575; U = 51,517; FDR-p = 0.002; δ = 0.202), nGirth also shows a significant advantage (0.595 vs. 0.542; U = 51,940; FDR-p = 0.002; δ = 0.211), and nPerimeter confirms the same pattern (0.660 vs. 0.611; U = 50,316; FDR-p = 0.008; δ = 0.174). nDispersion exhibits a small but significant effect in favor of Yazd (0.742 vs. 0.718; U = 49,054; FDR-p ≈ 0.031; δ = 0.144). Other indices—including nProximity, nCohesion, nTraversal, nExchange, nRange, nDetour, and nInterior—do not remain significant after FDR correction. The spatial reading of the maps is consistent with the statistics: in Yazd, the upper deciles of nDepth, nGirth, and nPerimeter appear as continuous clusters in the historic core and along the main axes (indicating introversion and compact cores). In Amol, higher values tend to be more strip-like or peripheral, aligned with open/blue corridors (reflecting openness for ventilation and moisture removal). Climate thus generates significant differences in morphological depth and edge efficiency, while network efficiency in both fabrics converges to a relatively similar level. The practical implication for conservation and design is that in Yazd, priority should be given to preserving compact cores, maintaining continuous shade, and controlling edge roughness; whereas in Amol, preserving wind corridors and the continuity of open spaces, alongside increasing the morphological depth of shallow cores (without undermining permeability), becomes a key objective.