Introduction
Rapid growth of urban peripheral settlements in recent decades has become one of the most significant challenges facing urban management. The physical expansion and population increase in these areas have placed substantial pressure on urban resources, infrastructure, and spatial structures. Under such conditions, the effectiveness of urban planning in guiding and controlling these trends plays a decisive role in achieving balanced and sustainable development.
The present study was conducted with the aim of identifying the factors influencing the effectiveness of urban planning in controlling the physical and population growth of urban peripheral areas in Zahedan.
Zahedan has experienced rapid and unbalanced population growth and physical expansion over recent decades. Much of this growth has occurred outside the framework of formal planning, manifested in horizontal, dispersed, and predominantly urban peripheral development. An examination of population trends shows that the city’s population increased from about 70,000 in 1976 to more than 735,000 in 2023 an over tenfold rise in less than five decades. This demographic surge, accompanied by large‑scale migration and structural transformations, has driven rapid physical expansion, increasing the city’s legal area from approximately 25 square kilometers to more than 85 square kilometers.
However, a significant portion of this expansion has taken place in urban peripheral and marginal areas, often informally, without legal documentation, and in the absence of spatial planning principles. According to official reports, more than 40 percent of Zahedan’s settlements are located in the urban fringe and lack access to basic urban services such as water supply, sewerage networks, transportation infrastructure, and educational and healthcare services. This situation reflects a substantial gap between the city’s actual development and the objectives of approved master and detailed plans. For instance, the actual population in 2021 exceeded master plan projections by more than 100,000 people, and proposed development zones have been largely disregarded in practice due to informal construction and weak enforcement.
In the realm of urban management, challenges such as limited financial resources, the absence of an effective land and housing control system, weak implementation of spatial plans, and poor coordination among relevant institutions have further reduced the effectiveness of mechanisms intended to manage physical and population growth in urban peripheral areas. The consequences of these conditions include uneven population distribution, the expansion of informal settlements, declining quality of the living environment, and intensifying socio‑economic vulnerabilities along the urban fringe.
Given these conditions, the central question of this research is: What factors influence the effectiveness of urban planning in Zahedan in controlling physical and population growth, particularly in urban peripheral areas? Identifying the institutional, managerial, structural, and spatial components underlying this inefficiency and assessing the alignment between actual developments and adopted urban planning policies can serve as an important step toward reforming spatial planning and achieving more balanced and sustainable development in Zahedan.

Methodology
This applied research employed a mixed‑method (qualitative–quantitative) approach, using interviews and questionnaires as data collection tools. Data were gathered through in‑depth semi‑structured interviews with 30 professors and experts selected via purposive sampling. Data analysis was carried out using the Grounded Theory method through open, axial, and selective coding, along with the Friedman test.

Results and discussion
The results showed that the set of causal factors includes population pressures, shortage of formal housing, inefficiency of the land management system, and weaknesses in urban planning. Additionally, the environmental characteristics of Zahedan, the region's socio-economic status, the physical context, and the position of local institutions were identified as contextual factors, while the categories of urban governance quality, legal and regulatory status, stimulating economic factors, and government interventions were classified as intervening factors. Finally, based on the Friedman test results, the factor of the region's socio-economic status ranked first with a mean rank of 8.45, indicating that economic issues, poverty, unemployment, and residents' living conditions have the greatest impact on the process of settlement expansion in peri-urban areas. Following that, the inefficiency of the land management system with a rank of 8.42 and population pressures with a rank of 8.34 were placed in subsequent priorities, reflecting the important role of land management, land distribution and ownership patterns, as well as population and its effects in directing or intensifying informal developments.

Conclusion
The findings indicate that the development of informal settlements in the peri-urban areas of Zahedan results from the systemic interaction of three categories of factors: causal, contextual, and intervening. Based on the Friedman test ranking, the socio-economic factor, with the highest rank, has the greatest impact, revealing that structural poverty, chronic unemployment, and livelihood insecurity act as the main driving forces, pushing populations toward areas where the minimum cost of shelter is achievable. This finding supports the theory of economic push factors and demonstrates that affordable housing in peri-urban areas is not a choice but a livelihood necessity. In the second rank, land system inefficiency, with a statistically narrow gap from the top rank, indicates a strong correlation between economic issues and land management. Scientifically speaking, this inefficiency including land speculation, ambiguous ownership, and cumbersome regulations has created a black market for land, making formal land inaccessible on one hand while placing unregulated and cheap peri-urban land within the reach of the poor on the other.