Strategies for Enhancing the Urban System of Gilan Province through a Spatial Planning Approach

Introduction: 
Accordingly, analyzing the urban system of Guilan Province—with an emphasis on urban population dynamics, hierarchical structures, and trends of spatial concentration and balance between 1986 and 2021—provides essential insights into the province’s spatial development challenges and potential pathways for future development. The main research questions are as follows:

1. How has the structure and transformation of Guilan’s urban system evolved over the past half-century?
2. What factors have contributed to the formation and persistence of spatial centralization in the province?
What strategies can be proposed, within a spatial planning framework, to enhance spatial and functional balance across Guilan’s urban network?

Methodology: This study is applied and analytical in nature and employs a descriptive–analytical and comparative approach to examine the structure and evolution of the urban system of Guilan Province between 1986 and 2021. The objective is to identify trends in urban concentration and population distribution and to propose spatial balancing strategies within the framework of spatial planning. The research data consist of population figures for all cities in the province across five official national census years. Data were obtained from the Statistical Center of Iran and provincial statistical yearbooks and were processed using Excel. Urban population was treated as the primary indicator of each city's position within the urban hierarchy. The analytical process consisted of four stages:

Analysis of changes in urban population;
Examination of the hierarchical structure;
Assessment of spatial concentration and balance;
Formulation of spatial balancing strategies.

planning. To analyze the data, a comprehensive set of quantitative urban-system models was employed. The Primacy Index, Ginsberg Index, Mehta Index, Herfindahl–Hirschman Index (HHI), and MOMA Index were used to assess concentration at the upper levels of the urban hierarchy. The Entropy Index was applied to measure spatial balance, while the Elasticity Model was used to analyze the dynamics of urban population change. Numerical calculations and the plotting of rank–size distributions and concentration curves were performed using Excel.
Results:  The analysis of demographic and spatial indicators from 1986 to 2021 indicates that Guilan Province’s urban network underwent a gradual transition from a monocentric, Rasht-dominated structure toward a relatively more balanced polycentric system. During the early years (1986 and 1996), the urban population was highly concentrated in Rasht, while other cities played only a limited role in shaping the province’s spatial structure. Over time, however, economic development, improvements in transportation networks, the establishment of industrial zones, and the expansion of services in medium-sized cities contributed to a decline in population concentration and a more even distribution of population across large and medium-sized urban centers. The Entropy Index decreased slightly from 0.723 in 1986 to 0.693 in 2021. Despite this modest decline, when interpreted alongside the other indicators, it suggests increased diversity and a more balanced spatial distribution of population. The Primacy Elasticity Index increased from 0.369 to 0.422, reflecting reduced concentration in the primate city and gradual population growth in second-tier cities, particularly Bandar Anzali, Lahijan, and Talesh. The Mehta and Ginsberg indices also reveal movement toward a more balanced hierarchical structure. The Mehta Index increased from 0.629 in 1986 to 0.697 in 2021, while the Ginsberg Index rose from 1.693 to 2.302, indicating strengthened roles for medium-sized cities and a gradual reduction in Rasht’s absolute dominance. Similarly, the Herfindahl–Hirschman Index (HHI) increased from 0.162 in 1986 to 0.197 in 2021, signaling reduced extreme concentration and greater spatial competitiveness among cities. The MOMA Index declined from 2.652 to 2.541, demonstrating increased cohesion and relative equality among city sizes. Finally, the Primacy and Bi-City indices provide additional insight. The Primacy Index (the population of the largest city relative to that of the second-largest city) increased from 0.369 to 0.422, while the Bi-City Index (the combined population of the two largest cities relative to the total urban population) rose from 3.445 to 5.996. These changes indicate that although Rasht continues to function as the leading urban center, the second- and third-ranked cities have increasingly absorbed a substantial share of urban growth.
Discussion: The longitudinal analysis of demographic and spatial indicators demonstrates a gradual transformation of Guilan’s urban network from a Rasht-centered monocentric structure toward a more balanced and emerging polycentric pattern. Population concentration has moderately declined, while the functional roles of medium-sized cities—such as Bandar Anzali, Lahijan, and Talesh—have expanded. The combined results of the Entropy, Mehta, Ginsberg, HHI, MOMA, and Primacy indices indicate increased spatial convergence, reduced dominance of the primate city, and enhanced multinucleation within the provincial urban system. This evolving spatial configuration creates opportunities to improve the distribution of services, achieve a better balance between employment and housing, and reduce urban pressures on Rasht.
Conclusion: The analysis of demographic and spatial trends between 1986 and 2021 provides a comprehensive understanding of the transformations that have occurred within Guilan Province’s urban system. Calculations of key indices—including the Entropy, Mehta, Ginsberg, Herfindahl–Hirschman, MOMA, Primacy, and Bi-City indices—demonstrate a structural transition from a centralized monocentric system toward a more diverse, dynamic, and relatively balanced spatial pattern. Medium-sized and smaller cities have increasingly absorbed population and economic functions, while the dominance of the primary urban center has gradually weakened. This shift reflects an evolving spatial logic in the distribution of population, resources, and capital and indicates a gradual weakening of long-standing centralization tendencies. Based on these trends, and drawing on both quantitative findings and spatial analysis, it is possible to address the key research questions concerning the structure and transformation of the urban system, the drivers of spatial centralization, and appropriate strategies for achieving spatial balance within a spatial planning framework.
In summary, over the past five decades, Guilan’s urban system has evolved from a predominantly centralized structure toward a more polycentric configuration. Although this transition has established the foundations for greater spatial balance, achieving a fully efficient, interconnected, and sustainable urban network will require reforms in spatial policy, more equitable resource allocation, and stronger institutional coordination among cities. The future of the province’s spatial development depends on regional planning approaches that prioritize not only physical growth but also spatial justice, environmental sustainability, and functional synergy among urban centers.