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The historically developed area of Istanbul will be analyzed with conventional space syntax approach and its extended version. The topography of the study area is rich in height variation. To analyze urban forms on a three-dimensional surface, space syntactic idea is extended in two aspects. The notion of axial lines is extended to incorporate the height change by introducing “extended axial lines”. Moreover, a weighting function is introduced to represent the overlapping nature of inter-visible areas between two neighboring axial lines. Space syntactic indices related to local centeredness are calculated and compared to indices representing actual urban activities. The results indicate that space syntactic indices extended to three-dimensional space capture well the concept of the amount of buildings and commercial activities along roads, whilst they fail to capture the concept of experts ’ indication of local centers. The space syntax approach emphasizes the mutual visibility, which may not be the principal factor in forming traditional cities, such as Islamic cities. This result, therefore, suggests that another principal factor should be sought in building of a powerful analyzing tool for such traditional cities. Compared to the extension to three-dimensiona