Introduction
The rapid growth of urbanization, increasing population density, and the concentration of vital activities in cities have significantly heightened the vulnerability of urban spaces to various natural and human-made hazards. In this context, metropolitan areas, due to the complexity of their physical structure, high population density, concentration of critical infrastructures, and strategic role within the national urban network, are more exposed to security threats and multiple crises than other settlements. Urban emergency shelters, as one of the most effective tools for reducing human casualties and enhancing urban resilience, play a key role in crisis management and urban defense. However, the effectiveness of these spaces is highly dependent on scientific, purposeful site selection that is compatible with the city’s physical, demographic, environmental, and security conditions. In this regard, the passive defense approach, with its emphasis on reducing vulnerability, ensuring the continuity of vital functions, and protecting citizens’ lives against natural and human-made threats, provides a strategic framework for the location of urban shelters. A review of the research background indicates that although numerous studies in Iran have addressed the site selection of urban shelters from a passive defense perspective, most of these studies have focused on central metropolises or border cities, while Shiraz, as a major metropolis in the south of the country, has received relatively limited attention. Moreover, the absence of a systematic synthesis of criteria and indicators used in domestic studies underscores the necessity of conducting a combined study employing a systematic review and spatial analysis approach.

Methodology
The present study is applied in terms of purpose and descriptive–analytical in nature, and it was conducted using a multi-criteria decision-making approach and spatial analyses within a Geographic Information System (GIS) environment. The study area is District 10 of Shiraz Municipality, selected as the largest urban district of this metropolis and one of the main centers of population and physical development in the northwest of the city. Research data were collected through a library–field method. In the first stage, through a systematic review and synthesis of 20 domestic scientific–research articles related to the site selection of urban shelters from a passive defense perspective, the effective criteria and indicators were extracted and integrated. Accordingly, ten final indicators were identified across four dimensions: demographic, physical, environmental–natural, and functional. In the next stage, the information layers for each indicator were prepared and updated using data from Shiraz Municipality’s comprehensive and detailed plans as well as OpenStreetMap data. Subsequently, to weight the criteria and indicators, the Fuzzy Analytic Hierarchy Process (FAHP) was applied based on the opinions of ten experts in the fields of geography, urban planning, crisis management, and passive defense. After standardizing the layers using fuzzy membership functions and applying the weights, the layer overlay process was carried out using the Fuzzy Overlay tool in the GIS environment, and ultimately, the zoning map of the most suitable locations for the establishment of urban shelters was produced.

Results and discussion
The results of the weighting of criteria indicated that demographic and security indicators hold the greatest importance in the site selection of urban shelters. Accordingly, the indicator of “high population density areas,” with a weight of 0.167, and “distance from potential enemy targets,” with a weight of 0.142, received the highest priorities. This finding suggests that protecting large population concentrations and avoiding the placement of shelters in proximity to sensitive and potentially military targets are among the most critical considerations of passive defense at the urban scale. Subsequently, the indicators of “population-attracting centers” and “proximity to centers with supportive functions during crises,” each with a weight of 0.124, play a decisive role in enhancing the efficiency and accessibility of shelters. In contrast, indicators such as “land slope” (0.057) and “access to urban open spaces” (0.043) were assigned lower priorities. The results of the spatial analysis and layer overlay revealed that the most suitable zones for the establishment of urban shelters are mainly concentrated in Golestan Town and parts of Beheshti Town. These zones achieved the highest suitability scores in the final model due to the simultaneous presence of high population density, major population-attracting centers such as universities and large commercial complexes, adequate coverage of supportive land uses, and an urban road network with good accessibility and multiple alternative routes. These results are consistent with the findings of domestic studies and, at the same time, place greater emphasis on the importance of security and functional indicators compared to foreign studies, which have predominantly focused on natural hazards.

Conclusion
The present study demonstrates that the site selection of urban emergency shelters based on a passive defense approach requires a perspective that goes beyond purely natural and physical criteria, and that simultaneous attention to demographic, security, and functional dimensions plays a decisive role in enhancing the effectiveness of these spaces. The findings can serve as a scientific basis for decision-making by urban managers and responsible institutions in planning for urban safety and resilience. Nevertheless, limitations such as access to up-to-date data, the limited number of experts, and the lack of analysis of different threat scenarios constitute some of the challenges of the present research. It is recommended that future studies employ dynamic data, multiple threat scenarios, and more advanced hybrid models, and that other districts of the Shiraz metropolis as well as cities in the southern regions of the country be examined.

Keywords
Urban Emergency Shelters, Passive Defence, FAHP method, Geographic Information Systems (GIS), Shiraz

Funding
There is no funding support.

Authors’ Contribution
Authors contributed equally to the conceptualization and writing of the article. All of the authors approved thecontent of the manuscript and agreed on all aspects of the work declaration of competing interest none.

Conflict of Interest
Authors declared no conflict of interest.

Acknowledgments
We are grateful to all the scientific consultants of this paper.