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Volume 38, Issue 2 (2023)
GeoRes 2023, 38(2): 191-201 |
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Received: 2022/12/8 | Accepted: 2023/01/30 | Published: 2023/06/5
Received: 2022/12/8 | Accepted: 2023/01/30 | Published: 2023/06/5
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Riazi H, Haghighatnaeini G, Dadashpour H. Spatial-Functional Structure in Connection with the Quality of Sustainable Urban Accessibility (Case Study: Enghelab Islami Square Area in The Tehran Metropolitan). GeoRes 2023; 38 (2) :191-201
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1- Department of Urban Planning, Faculty of Art and Architecture, University of Art, Tehran, Iran
2- Department of Urban Planning, Faculty of Art and Architecture, Tarbiat Modares University, Tehran, Iran
2- Department of Urban Planning, Faculty of Art and Architecture, Tarbiat Modares University, Tehran, Iran
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Introduction
Urban transportation exerts profound effects on the local and global environment, quality of life, and the socio-economic performance of cities [Newman & Kenworthy, 1999]. The concept of accessibility is one of the most important and frequently discussed notions in achieving the objectives of urban transportation. Inspired by the definition of “potential” in gravity theory, Hansen defined accessibility as the “potential of opportunities for interaction,” measured by the relative proximity from one location to another or from one group of people to another [Hansen, 1959]. Accessibility has also been described as an advanced form of centrality within the spatial structure of a city, rooted in location theory [Shen, 2017]. Furthermore, accessibility can be defined as the ease and convenience of reaching spatially distributed opportunities through the choice of a given transport mode [Dong et al., 2006]. Elements such as the probability of access through a specific transport mode [Dalvi & Martin, 1976], the richness of available choices [Berechman, 1981], and the benefits derived from improved services and facilities [Ben-Akiva & Lerman, 1979] have all been central in shaping the definition of accessibility. As the ultimate goal of transportation, accessibility is a key concept in understanding the interrelationship between transport and land use, as well as their combined impacts. Indeed, transport enhances the spatial interrelations among activities and land uses, including the capacity of urban places to attract and the ease of reaching them [Handy, 1993]. Across these definitions, two essential dimensions, opportunities and facilities, as well as the manner or cost of reaching them, are emphasized. These dimensions, on the one hand, concern urban land uses and activities, and, on the other hand, the systems of urban transportation. By reversing this assumption and considering an even distribution of urban opportunities, it can be shown that the distance between opportunities corresponds to accessibility on a more refined scale within spatial segregation models. Some characteristics of such accessibility models, based on network analysis, emerged in the 1950s and 1960s with the introduction of graph theory into geography. However, graph-based accessibility indices have been less explored in transport research compared to studies in the built environment [Shen, 2017].
With the emergence of the sustainability paradigm in various discourses, the relationship between accessibility and sustainability has been increasingly examined under the concept of sustainable urban accessibility. This involves improving conditions for greater reliance on environmentally friendly modes of urban mobility, such as walking, cycling, rail-based transit, and clean vehicles, while maintaining and enhancing the range and diversity of accessible urban activities within an acceptable time frame [Bertolini et al., 2005].
As indicated, one of the main elements in evaluating accessibility and sustainable accessibility is the spatial structure of activities and transport infrastructures. The concept of urban structure has been applied in studies of varying scales, domains, and interdisciplinary contexts with diverse aims. In urban studies, structural features typically refer to density, land use arrangements, distances between urban centers, their interconnections, and the infrastructures that support urban mobility [Marquez & Smith, 1999]. According to Živković, urban structure refers to the pattern or organization of blocks, streets, buildings, open spaces, and landscapes that together shape urban areas, and it reflects the interrelationships among all these elements [Živković, 2018]. More specifically, spatial structure refers to the spatial distribution of internal elements and the interactions of urban factors within the city system, including both physical and perceptual environments such as the socio-economic context [Anas et al., 1998; Li et al., 2018]. Sohn defines urban spatial structure as the spatial distribution and density patterns of economic activities and settlements along existing transport networks, which, in turn, influence urban spatial distribution. He emphasizes that understanding these spatial patterns is essential for predicting the development of urban transport systems [Sohn, 2015]. Similarly, Krehl describes urban spatial structure as recognizable patterns in the distribution of human activities across urban areas [Krehl, 2015].
Overall, urban structure expresses the location and organization of natural and artificial elements, as well as land-use patterns. These natural and artificial elements include axes, zones, and major nodes or centers that shape the overall structure of cities [Fujita et al., 1999]. Based on this concept, the principal components of urban structure can be assessed in two dimensions: some pertain to functional characteristics, while others relate to morphological or spatial features [Acheampong, 2020]. The morphological dimension concerns the distribution of centers, i.e., the pattern of local nodes, whereas the functional dimension concerns the interactions among nodes, such as commuting flows or trade linkages.
From a morphological perspective, urban structure has been defined as a combination of multiple physical characteristics of urban form, including land-use composition, city size, density, and spatial clustering, as determined by planners, economists, geographers, and other policymakers. In this respect, it is linked to the layout of public and private spaces, as well as the quality of connectivity and accessibility [Boarnet & Wang, 2019]. A key theory in this domain is space syntax, which describes the spatial system as a continuous network wherein spatial segments interconnect as an integrated whole [Hillier & Hanson, 1984; Hillier, 1996]. Hillier argues that the social meanings of urban spaces, as a form of social order, are expressed through the interactions among spaces, measured by the geometric properties of the spatial network. In space syntax models, the computation of spatial connections serves as a means of understanding their social and cultural significance [Hillier & Vaughan, 2007]. Space syntax is sometimes referred to as the “third form of accessibility” [Batty, 2009], as it emphasizes the physical connectedness of built urban spaces to one another. Hillier contended that urban flow patterns, determined by spatial configuration, drive land-use changes, thereby shaping urban performance. This reasoning clarifies the theoretical role of urban design in mediating the interaction between land-use patterns and urban movement, and it provides a valuable reference for subsequent urban studies on the spatial functioning of cities from a design perspective [Hillier, 1996].
The aim of this study was to examine the functional–spatial structure using spatial analysis methods.
Methodology
The present study is of a developmental and applied nature, conducted in 2022 with a quantitative approach in the area of Enghelab-e Eslami Square, Tehran metropolis. For spatial analyses, Geographic Information System (GIS)-based methods such as urban network analysis and space syntax analysis were employed to examine the integration of urban axes. Data on building units, land use, and the road network were obtained from the approved detailed plan of Tehran (2011) and subsequently updated through field surveys and aerial maps.
The analyses were carried out in four main stages:
Stage 1. Functional structure mapping
The functional structure of the study area was identified, including Points of Interest (POIs) and transport nodes. POIs were selected based on two criteria: (1) urban or supra-urban scale of activity, and (2) high trip attraction measured by the number of visitors. Activities with an urban-scale function but low visitor numbers were excluded from this category.
Stage 2. Spatial integration analysis
To evaluate and compare the integration of urban axes and spatial accessibility of urban blocks, network analysis and space syntax were applied. Within the space syntax framework, the axial line method was used to describe spatial configurations and the connected network. Axes with the highest degree of global integration were identified as primary axes. Spatial accessibility of urban blocks was then assessed using network analysis based on pedestrian pathways within the GIS environment. In this analysis, each block was modeled as a node in the graph, and its distance from other blocks within a 500-meter pedestrian radius was calculated. Blocks with access to a higher number of adjacent blocks within this radius were defined as the most spatially accessible.
Stage 3. Functional–spatial coordination
The degree of coordination between the functional–spatial structure and sustainable transport infrastructure was examined through the proximity of POIs to urban transport stations. Specifically, POIs located within a 100-meter functional radius from the main axes were identified, and the percentage of activity and transport nodes falling within this boundary was calculated.
Stage 4. Sustainable urban accessibility assessment
To assess sustainable urban accessibility, service area analysis within the GIS framework was performed. Sustainable transport infrastructures were categorized into two levels:
For the analyses, one core area and one immediate surrounding area were defined. The core area contained the POIs and transport infrastructures, while the surrounding area included the building units located within walking distance of public transport stations. The study area was bounded by Keshavarz Boulevard to the north, Jomhouri Eslami Street to the south, Vahid Highway to the west, and Valiasr Street to the east.
Findings
The structural elements related to the concept of sustainable accessibility, including Points of Interest (POIs) and sustainable urban transport stations, were analyzed as the functional structure of the study area. According to the results of the space syntax analysis using the axial line method, Enghelab-e Eslami, Kargar, Jomhouri, Valiasr, Towhid, Felestin, and Jamalzadeh streets demonstrated the highest levels of integration, while other urban collector and distributor axes showed relative integration with adjacent routes.
The highest spatial accessibility was observed in the northwestern section, while the lowest was detected in the southwestern section of Enghelab Square. This outcome was influenced by factors such as the design of the urban fabric, block dimensions, and the connectivity of the street network, and it illustrated the permeability of the urban fabric.
Based on this, a 100-meter functional radius from the main axes was used to align the functional–spatial structure with three components: POIs, block characteristics, and the urban street network. Results revealed that 11 out of 42 POIs (approximately 25%) were not located along the main axes with high integration. These points were concentrated in the northwestern section of Enghelab Square. Two major centers including Tehran University and Imam Khomeini Hospital were positioned around the main axes of Enghelab, Towhid, and Jamalzadeh streets.
Sustainable urban transport infrastructures (metro and BRT stations) were generally aligned with the main axes, while some bus stops and bicycle parking facilities were situated around moderately integrated routes such as Keshavarz Boulevard. This was consistent with their lower functional level.
Regarding the relationship between block spatial accessibility and the location of POIs, a mismatch was identified. The highest concentration of POIs was found in the northeastern section of Enghelab Square, around Vesal, Taleghani, and Italia streets, which were relatively less accessible. Conversely, the intersection of Enghelab and Jamalzadeh streets showed high spatial accessibility but a low concentration of POIs. The southeastern section of Enghelab Square exhibited relatively high spatial accessibility along with a moderate concentration of urban activities. Overall, about 70% of POIs were located in areas with relatively favorable spatial accessibility when comparing the functional and spatial structures.
For evaluating sustainable accessibility, transport stations were classified into two levels:
Out of 6,938 building parcels in the study area, 5,331 parcels (about 75%) were located within the service radius of Level 1 transport stations. Weak accessibility was identified in the northern section around Keshavarz Boulevard and in the southern section near certain parts of Jomhouri Street. Bicycle-sharing stations and bus stops (Level 2 infrastructures) were generally situated within the service areas of metro and BRT stations, indicating good integration with public transport systems, although their distribution within the urban fabric was uneven. Level 2 sustainable transport infrastructures covered approximately 85% of the study area. Areas outside their service coverage were primarily internal sections of urban blocks. This was particularly evident in the northwestern section near Jamalzadeh Street, the northeastern section near Vesal Street, and the southeastern section around Shahid Ravanmehr and Shahid Nazari streets. From the perspective of urban activities, most POIs fell within the functional radius of these infrastructures, with only a few exceptions around Qods and Vesal streets and one along Felestin Street.
Discussion
The findings of this study addressed two main objectives. The first objective was to analyze the alignment of the spatial structure of Points of Interest (POIs) and sustainable urban transport stations with the spatial structure of main axes, in terms of functional–spatial coordination. The results indicated that, with the exception of areas around Italia Street, Vesal Street, and Keshavarz Boulevard in the northeastern part of Enghelab-e Eslami Square, a relative alignment exists between spatial accessibility of the axes and the functional structure. Furthermore, when comparing block-level spatial accessibility with the distribution of POIs, it was observed that, despite the high concentration of POIs in the northeastern part of Enghelab Square, spatial accessibility was more favorable in the southeastern and northwestern areas. This outcome is consistent with the findings of Shen and Karimi, who demonstrate that spatial centrality and functional centrality dynamically influence each other, such that their interaction cannot be disregarded in shaping urban development across different scales [Shen & Karimi, 2018].
The second objective was to evaluate sustainable urban accessibility by assessing the extent to which the functional structure, comprising POIs and transport stations, was located within the service radius of public transport infrastructures. Regarding the accessibility of POIs to public transport stations, which relates to external-origin trips destined for major activity centers within the study area, the results revealed relatively favorable coverage. Similarly, accessibility of building parcels to both first- and second-level transport stations was assessed as relatively good, indicating adequate accessibility for residents. The similarity between the results of sustainable accessibility and functional–spatial coordination suggests that the alignment of these structures may play a critical role in enhancing the quality of sustainable urban accessibility. This has also been confirmed in the works of Gil, Bertolini, and Gharae et al., which highlight the impact of such alignment on achieving sustainability goals [Gil, 2016; Bertolini et al., 2005; Gharae et al., 2020]. For instance, the study by Clercq and Bertolini, which aligns closely with the present research, emphasize the role of environmental design principles in attaining sustainable urban accessibility and demonstrated how different urban areas, depending on the alignment of activity and transport characteristics, contributed to achieving accessibility goals [Clercq & Bertolini, 2003]. Similarly, Gil and Read highlight how variations in environmental features and transport networks across urban areas created different opportunities either to facilitate or hinder the adoption of sustainable mobility patterns, thereby influencing the quality of accessibility [Gil, 2012].
In line with the present study, other research has identified urban form indicators influencing transportation, including diversity, density, and design, along with accessibility and proximity to urban transport stations [Cervero & Kockelman, 1997; Ewing & Cervero, 2010]. Silva & Pinho, for example, develop a model to measure accessibility based on land-use diversity and relative accessibility to different transport modes, emphasizing the importance of these two components in assessing urban accessibility [Silva & Pinho, 2010].
Based on the results, the following recommendations are proposed to enhance the alignment of the functional–spatial structure with the objectives of sustainable urban accessibility:
Conclusion
A relative alignment between the functional–spatial structure and sustainable urban accessibility exists in the area surrounding Tehran’s Enghelab-e Eslami Square, indicating a relatively favorable condition.
Acknowledgments: No acknowledgments were reported by the authors.
Ethical Permission: No ethical approval was reported by the authors.
Conflict of Interest: The authors reported no conflicts of interest.
Author Contributions: Riazi H (First Author), Introduction Writer/Methodologist/Principal Researcher/Statistical Analyst/Discussion author (50%); Haghighatnaeini Gh (Second Author), Methodologist (25%); Dadashpour H (Third Author): Discussion Writer (25%)
Funding: This article is derived from the first author’s doctoral dissertation, conducted under the supervision of the second author and with consultation from the third author. All research costs were independently funded by the authors’ personal resources.
Urban transportation exerts profound effects on the local and global environment, quality of life, and the socio-economic performance of cities [Newman & Kenworthy, 1999]. The concept of accessibility is one of the most important and frequently discussed notions in achieving the objectives of urban transportation. Inspired by the definition of “potential” in gravity theory, Hansen defined accessibility as the “potential of opportunities for interaction,” measured by the relative proximity from one location to another or from one group of people to another [Hansen, 1959]. Accessibility has also been described as an advanced form of centrality within the spatial structure of a city, rooted in location theory [Shen, 2017]. Furthermore, accessibility can be defined as the ease and convenience of reaching spatially distributed opportunities through the choice of a given transport mode [Dong et al., 2006]. Elements such as the probability of access through a specific transport mode [Dalvi & Martin, 1976], the richness of available choices [Berechman, 1981], and the benefits derived from improved services and facilities [Ben-Akiva & Lerman, 1979] have all been central in shaping the definition of accessibility. As the ultimate goal of transportation, accessibility is a key concept in understanding the interrelationship between transport and land use, as well as their combined impacts. Indeed, transport enhances the spatial interrelations among activities and land uses, including the capacity of urban places to attract and the ease of reaching them [Handy, 1993]. Across these definitions, two essential dimensions, opportunities and facilities, as well as the manner or cost of reaching them, are emphasized. These dimensions, on the one hand, concern urban land uses and activities, and, on the other hand, the systems of urban transportation. By reversing this assumption and considering an even distribution of urban opportunities, it can be shown that the distance between opportunities corresponds to accessibility on a more refined scale within spatial segregation models. Some characteristics of such accessibility models, based on network analysis, emerged in the 1950s and 1960s with the introduction of graph theory into geography. However, graph-based accessibility indices have been less explored in transport research compared to studies in the built environment [Shen, 2017].
With the emergence of the sustainability paradigm in various discourses, the relationship between accessibility and sustainability has been increasingly examined under the concept of sustainable urban accessibility. This involves improving conditions for greater reliance on environmentally friendly modes of urban mobility, such as walking, cycling, rail-based transit, and clean vehicles, while maintaining and enhancing the range and diversity of accessible urban activities within an acceptable time frame [Bertolini et al., 2005].
As indicated, one of the main elements in evaluating accessibility and sustainable accessibility is the spatial structure of activities and transport infrastructures. The concept of urban structure has been applied in studies of varying scales, domains, and interdisciplinary contexts with diverse aims. In urban studies, structural features typically refer to density, land use arrangements, distances between urban centers, their interconnections, and the infrastructures that support urban mobility [Marquez & Smith, 1999]. According to Živković, urban structure refers to the pattern or organization of blocks, streets, buildings, open spaces, and landscapes that together shape urban areas, and it reflects the interrelationships among all these elements [Živković, 2018]. More specifically, spatial structure refers to the spatial distribution of internal elements and the interactions of urban factors within the city system, including both physical and perceptual environments such as the socio-economic context [Anas et al., 1998; Li et al., 2018]. Sohn defines urban spatial structure as the spatial distribution and density patterns of economic activities and settlements along existing transport networks, which, in turn, influence urban spatial distribution. He emphasizes that understanding these spatial patterns is essential for predicting the development of urban transport systems [Sohn, 2015]. Similarly, Krehl describes urban spatial structure as recognizable patterns in the distribution of human activities across urban areas [Krehl, 2015].
Overall, urban structure expresses the location and organization of natural and artificial elements, as well as land-use patterns. These natural and artificial elements include axes, zones, and major nodes or centers that shape the overall structure of cities [Fujita et al., 1999]. Based on this concept, the principal components of urban structure can be assessed in two dimensions: some pertain to functional characteristics, while others relate to morphological or spatial features [Acheampong, 2020]. The morphological dimension concerns the distribution of centers, i.e., the pattern of local nodes, whereas the functional dimension concerns the interactions among nodes, such as commuting flows or trade linkages.
From a morphological perspective, urban structure has been defined as a combination of multiple physical characteristics of urban form, including land-use composition, city size, density, and spatial clustering, as determined by planners, economists, geographers, and other policymakers. In this respect, it is linked to the layout of public and private spaces, as well as the quality of connectivity and accessibility [Boarnet & Wang, 2019]. A key theory in this domain is space syntax, which describes the spatial system as a continuous network wherein spatial segments interconnect as an integrated whole [Hillier & Hanson, 1984; Hillier, 1996]. Hillier argues that the social meanings of urban spaces, as a form of social order, are expressed through the interactions among spaces, measured by the geometric properties of the spatial network. In space syntax models, the computation of spatial connections serves as a means of understanding their social and cultural significance [Hillier & Vaughan, 2007]. Space syntax is sometimes referred to as the “third form of accessibility” [Batty, 2009], as it emphasizes the physical connectedness of built urban spaces to one another. Hillier contended that urban flow patterns, determined by spatial configuration, drive land-use changes, thereby shaping urban performance. This reasoning clarifies the theoretical role of urban design in mediating the interaction between land-use patterns and urban movement, and it provides a valuable reference for subsequent urban studies on the spatial functioning of cities from a design perspective [Hillier, 1996].
The aim of this study was to examine the functional–spatial structure using spatial analysis methods.
Methodology
The present study is of a developmental and applied nature, conducted in 2022 with a quantitative approach in the area of Enghelab-e Eslami Square, Tehran metropolis. For spatial analyses, Geographic Information System (GIS)-based methods such as urban network analysis and space syntax analysis were employed to examine the integration of urban axes. Data on building units, land use, and the road network were obtained from the approved detailed plan of Tehran (2011) and subsequently updated through field surveys and aerial maps.
The analyses were carried out in four main stages:
Stage 1. Functional structure mapping
The functional structure of the study area was identified, including Points of Interest (POIs) and transport nodes. POIs were selected based on two criteria: (1) urban or supra-urban scale of activity, and (2) high trip attraction measured by the number of visitors. Activities with an urban-scale function but low visitor numbers were excluded from this category.
Stage 2. Spatial integration analysis
To evaluate and compare the integration of urban axes and spatial accessibility of urban blocks, network analysis and space syntax were applied. Within the space syntax framework, the axial line method was used to describe spatial configurations and the connected network. Axes with the highest degree of global integration were identified as primary axes. Spatial accessibility of urban blocks was then assessed using network analysis based on pedestrian pathways within the GIS environment. In this analysis, each block was modeled as a node in the graph, and its distance from other blocks within a 500-meter pedestrian radius was calculated. Blocks with access to a higher number of adjacent blocks within this radius were defined as the most spatially accessible.
Stage 3. Functional–spatial coordination
The degree of coordination between the functional–spatial structure and sustainable transport infrastructure was examined through the proximity of POIs to urban transport stations. Specifically, POIs located within a 100-meter functional radius from the main axes were identified, and the percentage of activity and transport nodes falling within this boundary was calculated.
Stage 4. Sustainable urban accessibility assessment
To assess sustainable urban accessibility, service area analysis within the GIS framework was performed. Sustainable transport infrastructures were categorized into two levels:
- Level 1: metro stations and bus rapid transit (BRT) stations,
- Level 2: conventional bus stops and bicycle parking facilities.
For the analyses, one core area and one immediate surrounding area were defined. The core area contained the POIs and transport infrastructures, while the surrounding area included the building units located within walking distance of public transport stations. The study area was bounded by Keshavarz Boulevard to the north, Jomhouri Eslami Street to the south, Vahid Highway to the west, and Valiasr Street to the east.
Findings
The structural elements related to the concept of sustainable accessibility, including Points of Interest (POIs) and sustainable urban transport stations, were analyzed as the functional structure of the study area. According to the results of the space syntax analysis using the axial line method, Enghelab-e Eslami, Kargar, Jomhouri, Valiasr, Towhid, Felestin, and Jamalzadeh streets demonstrated the highest levels of integration, while other urban collector and distributor axes showed relative integration with adjacent routes.
The highest spatial accessibility was observed in the northwestern section, while the lowest was detected in the southwestern section of Enghelab Square. This outcome was influenced by factors such as the design of the urban fabric, block dimensions, and the connectivity of the street network, and it illustrated the permeability of the urban fabric.
Based on this, a 100-meter functional radius from the main axes was used to align the functional–spatial structure with three components: POIs, block characteristics, and the urban street network. Results revealed that 11 out of 42 POIs (approximately 25%) were not located along the main axes with high integration. These points were concentrated in the northwestern section of Enghelab Square. Two major centers including Tehran University and Imam Khomeini Hospital were positioned around the main axes of Enghelab, Towhid, and Jamalzadeh streets.
Sustainable urban transport infrastructures (metro and BRT stations) were generally aligned with the main axes, while some bus stops and bicycle parking facilities were situated around moderately integrated routes such as Keshavarz Boulevard. This was consistent with their lower functional level.
Regarding the relationship between block spatial accessibility and the location of POIs, a mismatch was identified. The highest concentration of POIs was found in the northeastern section of Enghelab Square, around Vesal, Taleghani, and Italia streets, which were relatively less accessible. Conversely, the intersection of Enghelab and Jamalzadeh streets showed high spatial accessibility but a low concentration of POIs. The southeastern section of Enghelab Square exhibited relatively high spatial accessibility along with a moderate concentration of urban activities. Overall, about 70% of POIs were located in areas with relatively favorable spatial accessibility when comparing the functional and spatial structures.
For evaluating sustainable accessibility, transport stations were classified into two levels:
- Level 1: metro stations and BRT stations with high passenger volumes,
- Level 2: bus stops and bicycle parking facilities with lower passenger volumes.
Out of 6,938 building parcels in the study area, 5,331 parcels (about 75%) were located within the service radius of Level 1 transport stations. Weak accessibility was identified in the northern section around Keshavarz Boulevard and in the southern section near certain parts of Jomhouri Street. Bicycle-sharing stations and bus stops (Level 2 infrastructures) were generally situated within the service areas of metro and BRT stations, indicating good integration with public transport systems, although their distribution within the urban fabric was uneven. Level 2 sustainable transport infrastructures covered approximately 85% of the study area. Areas outside their service coverage were primarily internal sections of urban blocks. This was particularly evident in the northwestern section near Jamalzadeh Street, the northeastern section near Vesal Street, and the southeastern section around Shahid Ravanmehr and Shahid Nazari streets. From the perspective of urban activities, most POIs fell within the functional radius of these infrastructures, with only a few exceptions around Qods and Vesal streets and one along Felestin Street.
Discussion
The findings of this study addressed two main objectives. The first objective was to analyze the alignment of the spatial structure of Points of Interest (POIs) and sustainable urban transport stations with the spatial structure of main axes, in terms of functional–spatial coordination. The results indicated that, with the exception of areas around Italia Street, Vesal Street, and Keshavarz Boulevard in the northeastern part of Enghelab-e Eslami Square, a relative alignment exists between spatial accessibility of the axes and the functional structure. Furthermore, when comparing block-level spatial accessibility with the distribution of POIs, it was observed that, despite the high concentration of POIs in the northeastern part of Enghelab Square, spatial accessibility was more favorable in the southeastern and northwestern areas. This outcome is consistent with the findings of Shen and Karimi, who demonstrate that spatial centrality and functional centrality dynamically influence each other, such that their interaction cannot be disregarded in shaping urban development across different scales [Shen & Karimi, 2018].
The second objective was to evaluate sustainable urban accessibility by assessing the extent to which the functional structure, comprising POIs and transport stations, was located within the service radius of public transport infrastructures. Regarding the accessibility of POIs to public transport stations, which relates to external-origin trips destined for major activity centers within the study area, the results revealed relatively favorable coverage. Similarly, accessibility of building parcels to both first- and second-level transport stations was assessed as relatively good, indicating adequate accessibility for residents. The similarity between the results of sustainable accessibility and functional–spatial coordination suggests that the alignment of these structures may play a critical role in enhancing the quality of sustainable urban accessibility. This has also been confirmed in the works of Gil, Bertolini, and Gharae et al., which highlight the impact of such alignment on achieving sustainability goals [Gil, 2016; Bertolini et al., 2005; Gharae et al., 2020]. For instance, the study by Clercq and Bertolini, which aligns closely with the present research, emphasize the role of environmental design principles in attaining sustainable urban accessibility and demonstrated how different urban areas, depending on the alignment of activity and transport characteristics, contributed to achieving accessibility goals [Clercq & Bertolini, 2003]. Similarly, Gil and Read highlight how variations in environmental features and transport networks across urban areas created different opportunities either to facilitate or hinder the adoption of sustainable mobility patterns, thereby influencing the quality of accessibility [Gil, 2012].
In line with the present study, other research has identified urban form indicators influencing transportation, including diversity, density, and design, along with accessibility and proximity to urban transport stations [Cervero & Kockelman, 1997; Ewing & Cervero, 2010]. Silva & Pinho, for example, develop a model to measure accessibility based on land-use diversity and relative accessibility to different transport modes, emphasizing the importance of these two components in assessing urban accessibility [Silva & Pinho, 2010].
Based on the results, the following recommendations are proposed to enhance the alignment of the functional–spatial structure with the objectives of sustainable urban accessibility:
- Increasing the connectivity and permeability of neighborhoods and districts to improve spatial accessibility;
- Locating POIs along central axes with the highest degree of integration, or within urban blocks characterized by high spatial accessibility and permeability;
- Positioning public transport stations, such as metro and Bus Rapid Transit (BRT) stations, adjacent to main integrated axes and major POIs;
- Ensuring adequate coverage of residential areas by sustainable urban transport stations, particularly second-level stations such as bus stops and bicycle-sharing facilities, which are more flexible in nature;
- Enhancing the integration between first- and second-level transport systems through the concept of multimodal transportation, thereby supporting the adoption of sustainable mobility patterns and improving coverage of internal residential areas through second-level stations.
Conclusion
A relative alignment between the functional–spatial structure and sustainable urban accessibility exists in the area surrounding Tehran’s Enghelab-e Eslami Square, indicating a relatively favorable condition.
Acknowledgments: No acknowledgments were reported by the authors.
Ethical Permission: No ethical approval was reported by the authors.
Conflict of Interest: The authors reported no conflicts of interest.
Author Contributions: Riazi H (First Author), Introduction Writer/Methodologist/Principal Researcher/Statistical Analyst/Discussion author (50%); Haghighatnaeini Gh (Second Author), Methodologist (25%); Dadashpour H (Third Author): Discussion Writer (25%)
Funding: This article is derived from the first author’s doctoral dissertation, conducted under the supervision of the second author and with consultation from the third author. All research costs were independently funded by the authors’ personal resources.
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