Urban Economics and Planning

Urban Economics and Planning

The Role of Natural Surveillance in Enhancing the Security of Public Spaces: A 3D Isovist Analysis of Sari’s 13-Pich Alley

Document Type : Original Article

Authors
Atiyeh Asgari 1
Hanieh Ziaratian 2
Arezoo Soltani 3
1 Assistant Professor, Department of Urbanism. ST.C., Islamic Azad University, Tehran, Iran
2 M.Sc. in Architectural Technology, Department of Architecture, Faculty of Architecture and Urban Planning, Iran University of Science and Technology, Tehran, Iran
3 B.Sc. in Architecture, Department of Architecture, West Tehran Branch, Islamic Azad University, Tehran, Iran
10.22034/uep.2025.525849.1649
Abstract
Introduction 
In recent decades, the security of urban public spaces has become a significant concern for urban designers, planners, and residents. One of the most important contemporary approaches in this regard is the concept of natural surveillance, which posits that spatial design can enhance visual and observational opportunities for indirect monitoring by citizens. This, in turn, can help prevent criminal activities. Rooted in the theories of Jeffrey Hill and Jane Jacobs, this approach is based on the principle that open and visible spaces are less likely to be misused. However, many urban spaces—particularly those within dense, historic urban fabrics—suffer from low levels of natural surveillance due to their physical structures. This can lead to a reduced sense of safety and increased vulnerability. The present study aims to introduce and apply an innovative approach for analyzing and enhancing natural surveillance in urban spaces. As a case study, it examines Kucheh-ye Sizdah-Pich (Thirteen-Turn Alley), located in the historical fabric of Sari, a city in northern Iran. Owing to its specific spatial characteristics, this alley is a clear example of a space with limited potential for natural surveillance, highlighting the urgent need for urban design interventions.
Materials and Methods
This study adopts a quantitative and analytical-simulation approach. To achieve the research objectives, the following steps were undertaken:
1. 3D Modeling: In the first step, the case study area—Kucheh-ye Sizdah-Pich (Thirteen-Turn Alley) located in the historical fabric of Sari—was modeled in high detail using Autodesk Revit. This precise 3D modeling formed the foundation for subsequent spatial analyses and enabled the examination of visual interactions within a virtual environment.
2. 3D Isovist Analysis: Advanced 3D isovist concepts were employed to conduct multilayer spatial analyses following the modeling phase. Isovists, or visibility maps, are powerful tools for assessing the visual field from a specific point in space. This study used analytical tools from Grasshopper—a powerful plugin within the Rhino software environment—to implement 3D isovist algorithms. These tools enabled precise visibility calculations from any desired point within the modeled space.
3. Programming and Data Analysis: Python was utilized to enhance the accuracy and flexibility of the analyses and automate complex processes. Python scripts were developed to process the data generated from the isovist analyses and perform more advanced computations. This stage included evaluating visibility from stationary and mobile observers (fixed viewpoints) (assessing the continuity of vision along movement paths), thus providing a comprehensive picture of the natural surveillance potential.
4. Visualization of Results: Finally, the outcomes of the spatial analyses and Python computations were graphically presented as heatmaps. These visualizations depict the degree of visibility along pathways from the perspective of observers, using color gradients that correspond to standard human visual ranges. This method of visualization greatly facilitated the interpretation and communication of the findings.
Findings
The analyses conducted through 3D modeling, isovist analysis, Grasshopper algorithms, and Python scripting revealed both the strengths and weaknesses of natural surveillance in Kucheh-ye Sizdah-Pich, located in the historical fabric of Sari. The resulting heatmaps differentiated between high and low visibility areas for both stationary and moving observers.
• Significant Reduction of Surveillance in Curved and Narrow Segments: The results clearly demonstrated a substantial decline in visibility—and consequently, in natural surveillance—in the narrow and winding segments of the alley. This reduction stems from visual obstructions caused by tall walls and sharp angles, which eliminate the possibility of visual continuity from one point to another. These areas were marked in red on the heatmaps, indicating minimal visibility.
• Fragmentation of Open and Limited Viewpoints: It was observed that even in relatively straight segments of the alley, open viewpoints were scattered and discontinuous due to the limited number and placement of doors, windows, and other openings. This discontinuity prevents the formation of a cohesive and effective natural surveillance network throughout the alley.
Conclusion
By introducing and applying an innovative approach to the analysis of natural surveillance, this study was able to quantitatively and precisely assess the visibility and surveillance potential of Kucheh-ye Sizdah-Pich in Sari as a case study. The results clearly indicated that the current spatial configuration of the alley leads to a low level of natural surveillance. However, these findings provide a solid foundation for proposing practical and evidence-based strategies to enhance both safety and spatial quality in this historic urban space:
• Increasing Openings and Transparency in Facades: It is recommended to introduce new openings—such as windows, skylights, or even decorative perforated screens—on the facades of buildings facing the alley. The use of transparent or semi-transparent materials in certain parts of the walls can also enhance visual connections for residents and pedestrians.
• Designing Open-View Green Spaces: The use of greenery that does not obstruct visibility—such as tall trees with high canopies or low-growing shrubs—can contribute to visual aesthetics while preserving natural surveillance.
• Improving Lighting and Nighttime Visibility: Since visibility naturally decreases at night, enhancing the alley’s lighting system can play a crucial role in increasing both surveillance and the perceived sense of safety.
• Encouraging Social Presence: Creating spaces for seating, social interaction, and small-scale local activities can encourage greater human presence in the alley, which in turn promotes natural surveillance through everyday social engagement.
This analytical method for enhancing safety is not only applicable to Kucheh-ye Sizdah-Pich, but also transferable to similar spaces within the historic fabrics of other cities. The use of advanced analytical tools such as 3D isovists and Python scripting provides a practical approach for precisely identifying spatial vulnerabilities and generating targeted urban design solutions. Ultimately, such methods hold significant potential for improving safety and vitality in public urban spaces.
Keywords
3D Isovist
Natural Surveillance
Urban Security
Visibility Analysis

Subjects

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Urban Economics and Planning
Volume 6, Issue 3
Summer 2025
Pages 118-129

  • Receive Date 25 May 2025
  • Revise Date 07 July 2025
  • Accept Date 13 July 2025