A Conceptual Model for Assessing the Relationship between Urban Morphology and Sustainable Urban Form

: The built environment witnessed rapid transformation after the industrial revolution. This transformation came along with some negativities, which gave rise to the concept of sustainability in urban form. In this regard, the current study aimed to assess and validate the reciprocal relationship between urban morphology and sustainable urban form. This study proposes a conceptual model which integrates and presents the holistic correlation between sustainable urban form and urban morphology, by using qualitative grounded theory as the research methodology. The model was developed by introducing analytical tools to evaluate sustainability, along with integrating typo-morphology and the concept of scale hierarchy. The ﬁndings of this study reveal that every single component of sustainable urban form interacts signiﬁcantly with the typo-morphology approach. Consequently, the outcomes help urban planners to get more informed decisions about the geometric analysis of urban morphology from a sustainability point of view.


Introduction
The emergence of the notion of sustainable development has created a platform to enable a public debate on the form of cities to take place [1]. It has subsequently motivated researchers, decision-makers, and urban planners in related disciplines to seek sustainable forms of development that are beneficial for the built environment. Considering this fact, morphological analysis of urban tissue reveals the logic of urban transformation, urban morphology can thus be a valuable implement to achieve sustainable urban form [2,3]. Although much research has been carried out on the topic of "urban sustainability" and "urban morphology", there seems to be a substantial gap in the study of the mutual relationship between the two [4][5][6][7][8]. This study tries to focus on the relations between urban morphology (UM) and a sustainable urban form (SUF). Accordingly, this study aims to propose a model to evaluate the relationship between SUF and UM. The analytical tools derived from this relationship can be used as an assessment technique.
Since the issue of the urban context is a continuous multi-layered process, it is vital to formulate a defined scale hierarch to streamline the process of the assessment. A strong spatial hierarchy is significant to determine the contribution between the important aspects of urban structure and the analytical tools of the research. Accordingly, the study introduces a spatially hierarchal structure, by integrating typo-morphology and the concept of scale hierarchy concerning Kropf's taxonomy [6].
Therefore, the following research question has been considered as the main concern of the research.

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What is the relationship between urban morphology (UM) and sustainable urban form (SUF)?

Literature Review
After World War II, the industrial revolution was unanimously embraced since it presented a global development that stretched and impacted numerous interwoven networks of dimensions such as sociocultural, religious, political, and economic [9,10]. Consequently, rapid industrialization and urbanization started to develop yet adverse effects on the built environment such as climate change, overuse of energy, pollution, and overpopulated urban centers [11]. As the numerous problems started to ascend, the notion of urban sustainability became the only alternative [1,[12][13][14]. In 1987, the imperative phrase

Literature Review
After World War II, the industrial revolution was unanimously embraced since it presented a global development that stretched and impacted numerous interwoven networks of dimensions such as sociocultural, religious, political, and economic [9,10]. Consequently, rapid industrialization and urbanization started to develop yet adverse effects on the built environment such as climate change, overuse of energy, pollution, and overpopulated urban centers [11]. As the numerous problems started to ascend, the notion of urban sustainability became the only alternative [1,[12][13][14]. In 1987, the imperative phrase of safeguarding resources for future generations in the "Brundtland Report" promoted the notion of "sustainable development" [15]. The focus of "sustainable development" is considering the provision of current requirements without jeopardizing offspring in meeting their requirements as next generation.
As Silva [13] states, urban form is a "spatial pattern" of individual activities at a defined time. Accordingly, sustainable urbanism improves not only people's living standards but also their safety [16]; however, it is confirmed that various urban structures may have different levels of sustainability [9,17]. There is also evidence to show that there is no single sustainable urban model acceptable in all circumstances [18]. The accessible data describe sustainability as a flourishing means of achieving equilibrium between environmental health, financial growth, and social equity. Therefore, this study attempts to formulate a framework to achieve an SUF. Since urban morphology provides a strong assessment tool for evaluating the built environment; this study used urban morphology as the base to achieve SUF. Consequently, the study conducts principles of SUF and UM to find out the relation.

Principles of Sustainable Urban Form (SUF)
Sustainable urbanism is required to be equipped with energy generation [19] and governance, water generation, waste management, design, engineering, architecture, equipment for sustainable construction and management of housing. Sustainable urban form, ideas, or principles are created and classified as: Greening, Mixed Land Uses, Sustainable Transport/Accessibility, Density, Passive Solar Design, Diversity, Permeability, Compactness, Legibility, and Imageability [1,20]. Each of these indicators has been considered to achieve sustainable urbanism ( Figure 2).

Principles of Sustainable Urban Form (SUF)
Sustainable urbanism is required to be equipped with energy generation [19] and governance, water generation, waste management, design, engineering, architecture, equipment for sustainable construction and management of housing. Sustainable urban form, ideas, or principles are created and classified as: Greening, Mixed Land Uses, Sustainable Transport/Accessibility, Density, Passive Solar Design, Diversity, Permeability, Compactness, Legibility, and Imageability [1,20]. Each of these indicators has been considered to achieve sustainable urbanism ( Figure 2).  The notion of SUF has been extensively discussed and is still under discussion. Alternatives include the compact city [39], decentralized concentration, remote new settlements [40] and multi-centric cities [17,41]. Jabareen [1] defines four types of SUF based on distinct design values; these sustainable urban types are Eco-City, Compact City, Urban  The notion of SUF has been extensively discussed and is still under discussion. Alternatives include the compact city [39], decentralized concentration, remote new settlements [40] and multi-centric cities [17,41]. Jabareen [1] defines four types of SUF based on distinct design values; these sustainable urban types are Eco-City, Compact City, Urban Containment, and Neo-traditional Development.

Principles of Sustainable
As Silva [13] notes, the entire idea of the urban form depends upon three factors which are the arrangement, appearance, and functionality of the buildings and structures. Fast-growing cities, on the other hand, are exposed to non-sustainable building plans and developments that lead to the exhaustion of resources and infrastructure. These are the consequences of the 'boom' in the construction sector, which requires and demands excessive resources. The invasion of rural areas for building purposes leads to deforestation, which involves the removal of thousands of hectares of trees, which also requires the construction of extensive transportation infrastructures. Furthermore, the growth of urbanism may also destroy the identity of urban areas, which are supporting specific types of lifestyle and culture. Thus, SUF is one of the methods that can provide safe growth and change without compromising natural sources or affecting social identity and culture [31].
Oliveira [3] stated the city has a multilayer system that analyzes the relationships of the physical and spatial aspects through four primary morphological layers of urban form which are: plot, buildings, street, and open space. Tadi et al. [42] gathered sustainable urban principles, including the primary layer of the systematic interpretation of the morphological methods of the city. The integration of the keys, such as analytical tools, creates a relationship between the different layers to improve the performance of the whole system ( Figure 3). Designers can use the keys whilst observing the process of design to analyze the context and the current condition and critical functionality of a city, before interfering. urban principles, including the primary layer of the systematic interpretation of the morphological methods of the city. The integration of the keys, such as analytical tools, creates a relationship between the different layers to improve the performance of the whole system ( Figure 3). Designers can use the keys whilst observing the process of design to analyze the context and the current condition and critical functionality of a city, before interfering.
As it is shown in Figure 3, these analytical tools which have been developed based on [25,26] comprise intensity (Density and Compactness), proximity (Sustainable Transport, Mixed Land Use), permeability, (imageability, legibility), Efficiency (greening, passive solar design), Accessibility (sustainable transport) and Diversity (legibility, mixed land use). According to Jabareen [1], there are general standards for developing SUF, which are related to the principles of SUF and morphological layers. From this point of view, it is essential to find out the relations among these concepts to formulate analytical tools for assessing sustainability in an urban context. The analytical tools are related to all the indicators of urban form, sustainable urban types, and the dimensions of SUF. The relationship between each factor of the analytical tools and each principle of SUF has been demonstrated in Figure 4. From this point of view, the combination is finding a connection amongst the global factors and design principles of SUF to devise analytical tools for sustainability in the urban form, related to all the indicators of urban form, sustainable urban types, and dimensions of SUF. As it is shown in Figure 3, these analytical tools which have been developed based on [25,26] comprise intensity (Density and Compactness), proximity (Sustainable Transport, Mixed Land Use), permeability, (imageability, legibility), Efficiency (greening, passive solar design), Accessibility (sustainable transport) and Diversity (legibility, mixed land use).
According to Jabareen [1], there are general standards for developing SUF, which are related to the principles of SUF and morphological layers. From this point of view, it is essential to find out the relations among these concepts to formulate analytical tools for assessing sustainability in an urban context. The analytical tools are related to all the indicators of urban form, sustainable urban types, and the dimensions of SUF. The relationship between each factor of the analytical tools and each principle of SUF has been demonstrated in Figure 4. From this point of view, the combination is finding a connection amongst the global factors and design principles of SUF to devise analytical tools for sustainability in the urban form, related to all the indicators of urban form, sustainable urban types, and dimensions of SUF.

Urban Morphology
According to Conzen [60] "Urban morphology" (UM) is expressed as the study of the formation of the built environment and the process of changes related to the spatial study of urban structures, land use, construction, open spaces, and road patterns. In this regard, Cowan [65] stated that UM is "the study of urban form" and identified four broad approaches to UM namely: 1. Historico-geographical; 2. Typo-morphological; 3. Spatialanalytical; 4. Configurational. UM and SUF holds different meanings for urban planners and designers, especially in developing cities. Accordingly, morphological studies can be divided into four groups considering various disciplines as geography, architecture, science, and philosophy. In respect of urban geography, the Conzeniana school of thought acts as a representation of ideas [66]. Caniggian School plays an important role in the discipline of architecture. Bill Hillier's Spatial Syntax explores the morphology of the city from a whole new perspective in the mathematical character that is related to power and science [67]. The philosophy of Henri Lefebvre  states that the urban area is not a neutral entity, it has a social existence and has designated areas to demonstrate or identify its society or culture ( Figure 5).

Urban Morphology
According to Conzen [60] "Urban morphology" (UM) is expressed as the study of the formation of the built environment and the process of changes related to the spatial study of urban structures, land use, construction, open spaces, and road patterns. In this regard, Cowan [65] stated that UM is "the study of urban form" and identified four broad approaches to UM namely: 1. Historico-geographical; 2. Typo-morphological; 3. Spatial-analytical; 4. Configurational. UM and SUF holds different meanings for urban planners and designers, especially in developing cities. Accordingly, morphological studies can be divided into four groups considering various disciplines as geography, architecture, science, and philosophy. In respect of urban geography, the Conzeniana school of thought acts as a representation of ideas [66]. Caniggian School plays an important role in the discipline of architecture. Bill Hillier's Spatial Syntax explores the morphology of the city from a whole new perspective in the mathematical character that is related to power and science [67]. The philosophy of Henri Lefebvre  states that the urban area is not a neutral entity, it has a social existence and has designated areas to demonstrate or identify its society or culture ( Figure 5). The approaches to typo-morphology can be said to have arisen from an urban and architectural perspective as well as historical-geographic and environmental analytical methods, which are derived from the geography sector [68,69]. Because the typo-morphological (typological process) has its roots in the fields of architecture and urbanism, the study will focus on typo-morphological approach. Hence, the historical-geographical and spatial-analytical factors, which are from the field of geography, will be neglected. Furthermore, space or configurational syntax will not be used because it has a mathematical or scientific origin rather than an architectural one and because this study is focused on the field of architecture. Since geometric analysis is an integral part of UM, the current study will deal with this assessment to provide valuable information for analyzing the physical elements of urban environments ( Figure 6).

Geometric Assessment Syntactic Assessment
Historico-Geographical approach Typo-morphological approach Spatial-analysis approach The Configurational approach Field of Geography

Field of Architecture Field of Science
Typo-m orphological approach Current study抯 concern Figure 6. The approaches for assessment of urban morphology in the relationship with SUF in the current study (developed by Authors).

Typo-Morphological Approach
Typo-morphological research has been used as a planning instrument throughout architectural history. The work of the Krier brothers [70] and Aldo Rossi [71] has been quite fruitful, especially in the context of the metropolitan fabric form, housing, and open spaces. As well as in respect to socioeconomic procedures. Typo-morphological surveys The approaches to typo-morphology can be said to have arisen from an urban and architectural perspective as well as historical-geographic and environmental analytical methods, which are derived from the geography sector [68,69]. Because the typo-morphological (typological process) has its roots in the fields of architecture and urbanism, the study will focus on typo-morphological approach. Hence, the historical-geographical and spatialanalytical factors, which are from the field of geography, will be neglected. Furthermore, space or configurational syntax will not be used because it has a mathematical or scientific origin rather than an architectural one and because this study is focused on the field of architecture. Since geometric analysis is an integral part of UM, the current study will deal with this assessment to provide valuable information for analyzing the physical elements of urban environments ( Figure 6).

Typo-Morphological Approach
Typo-morphological research has been used as a planning instrument throughout architectural history. The work of the Krier brothers [70] and Aldo Rossi [71] has been quite fruitful, especially in the context of the metropolitan fabric form, housing, and open spaces. As well as in respect to socioeconomic procedures. Typo-morphological surveys use construction information to define the city's physical shape and the method of human habitat accumulation, which helps gain knowledge of the city's three-dimensional structure and its fundamental development mechanism. As Moudon [72] notes: "typo-morphology provides a working definition of room and sort of construction, and acts as a wealthy starting point for learning the essence of building design, its connection with the town, and the community in which it occurs". Typo-morphological surveys are therefore not only useful for analyzing current cities or urban areas, but also for building the theoretical basis for urban design planning [73]. The methods derived from the studies carried out by the Italian architect Saverio Muratori, and further established by his disciples, Gianfranco Caniggia and Gian Luigi Maffei, are highly significant. The typological method focuses on the hypothesis that, by evaluating construction as the operational unit of an assessment, altering trends in urban form can then be better understood. This means that the typo-morphological approach, when applied to individual buildings and towns, considers using the geometrical analysis method. The components constitute the construction products for individual buildings, the construction of components conforms to the walls and the organization of the buildings. For cities, the area is comparable to that of morphological analysis, i.e., housing, urban tissues, and the various types of arrangement of urban tissues in a region or district [72,74]. Geographical scientists generally adopt the morphological classification, but architects tend to adopt the typo-morphological classification.

Methodology and Development of Conceptual Framework
The issue of urban formation as a dynamic process poses a challenge to current contexts and designers by taking into account the past in order to create the future. The urban formation is an ever-changing system and a continuous process in which many numbers of functional and geometric connections can be displayed at different levels or scales [75]. The morphological analysis of the urban fabric permits us to gain a logical understanding of their formation and transformation. Thus, the analysis assists us to design with authentic awareness and interventions within the process of change. Therefore, this study aims to streamline this complex system by expanding the concept of scale and hierarchy that are bound to each other. The concept must be discussed in terms of the relationships between spaces of different dimensions. In this case, the scale hierarchy is crucial because it affects the accuracy of the outcomes.
The urban morphology approach analyzes the built environment based on four main elements of the morphological layer in the study: buildings, streets, open spaces, and plots/lots. Moreover, the urban form can be understood from the perspective of four different levels or scales, which are commonly recognized. They are, namely: the region, the city, the street/block, and the building/lot [72]. The physical form describes the layers of the cities and the process of the accumulation of built environments, which helps in the definition of the city's three-dimensional structure and the process of city formation ( Figure 7). Therefore, this approach is not only suitable for the analysis of existing cities, but also for developing the theoretical base for urban design practice, since it has influenced urban development [73].
In the following part, the authors integrate the research design that proposes morphological dimensions for assessing SUF. The integrations will be based on two main combinations, the first is analytical tools by the integration between morphological layers and SUF principles, and the second is scale hierarchy and typo-morphology. The second combination will control the scale hierarchy of any case study when it is going to be evaluated and shows the effect of the scale hierarchy on the accuracy of the results. Finally, the findings will provide the experts with a tool to evaluate any part of the urban level starting from building to city scale, and permit them to assess the sustainability within the selected context.  In the following part, the authors integrate the research design that proposes morphological dimensions for assessing SUF. The integrations will be based on two main combinations, the first is analytical tools by the integration between morphological layers and SUF principles, and the second is scale hierarchy and typo-morphology. The second combination will control the scale hierarchy of any case study when it is going to be evaluated and shows the effect of the scale hierarchy on the accuracy of the results. Finally, the findings will provide the experts with a tool to evaluate any part of the urban level starting from building to city scale, and permit them to assess the sustainability within the selected context.

The Combination of Scale Hierarchy and Typo-Morphology
According to the division of process and the typological approach in the geometric assessment of urban morphology, the authors develop the combination of the relationship between the concept of scale hierarchy and the typo-morphology approach. There are various grades of spatial resolution in the built environment [80] that match to varying scales of perusal: buildings, urban fabric, cities, and regions [74]. According to Kropf's definition of urban morphology, the hierarchy of scales has been delineated into the following structure: materials form structures such as walls and roofs, and these structures then form rooms and corridors, etc., and ultimately combine to form a complete building. The concept is extending upward hierarchically and considers the building as an element to determine higher levels of the urban fabric. Kropf [6] has identified seven hierarchical grades (materials, architectural elements, buildings, lands, streets, blocks, and the fabric of the urban area); he debated that the dynamic relationship between these elements would influence the urban setting. Similarly, Kropf [81] proposes connections amongst the physical types based on a scale hierarchy, which is expressed on various scales. The objective is to establish a consistent basis for the definition and subdivision of the built form to support the concept of urban morphological analysis. The hierarchical divisions of the urban fabric are Minor, Mid, and Major.

The Combination of Scale Hierarchy and Typo-Morphology
According to the division of process and the typological approach in the geometric assessment of urban morphology, the authors develop the combination of the relationship between the concept of scale hierarchy and the typo-morphology approach. There are various grades of spatial resolution in the built environment [80] that match to varying scales of perusal: buildings, urban fabric, cities, and regions [74]. According to Kropf's definition of urban morphology, the hierarchy of scales has been delineated into the following structure: materials form structures such as walls and roofs, and these structures then form rooms and corridors, etc., and ultimately combine to form a complete building. The concept is extending upward hierarchically and considers the building as an element to determine higher levels of the urban fabric. Kropf [6] has identified seven hierarchical grades (materials, architectural elements, buildings, lands, streets, blocks, and the fabric of the urban area); he debated that the dynamic relationship between these elements would influence the urban setting. Similarly, Kropf [81] proposes connections amongst the physical types based on a scale hierarchy, which is expressed on various scales. The objective is to establish a consistent basis for the definition and subdivision of the built form to support the concept of urban morphological analysis. The hierarchical divisions of the urban fabric are Minor, Mid, and Major. a.
The Minor (Micro-scale) includes the following; 1. Materials: Materials provide a building with color and texture, the choice of materials also affects the issues of weathering, detailing, visual interest at various distances, and facade patterning [79,82,83].
2. Structure: The statement, 'structures are the single associations of several elements' defines the general classification at the second level. In referring to specific classes of structures, conventional terms such as floors, walls, partitions, roofs, etc., are used [84].
3. Building type: An organism of systems is the term used to refer to entities occupying the third level of the scale hierarchy. It is described generally as follows: aggregations or structures recognizable as relatively autonomous; elements like windows, doors, rooms, stairs, etc., that combine to form systems of the entire building [84]. 4. Rooms/Cells: Cells are combinations of structures that also have relative autonomy, e.g., rooms, stairs, etc. The conventional terms, 'rooms' and 'stairs' also refer to the base Sustainability 2022, 14, 2884 9 of 20 type and elementary cells, respectively. More specifically, the base type is defined as a single room dwelling of five or six square meters, comprising a single space enclosed by a floor, four load-bearing walls, and a roof in which a door is located for access [74].

b.
The Mid (Meso-scale) refers to the issue of urban tissue, which includes the following: 1. The Lots: The lot is defined as, 'the area built upon, together with the pertinent area'. The element that links built spaces to open spaces is the land lot or parcel, the primary cell of the urban fabric [38].
2. The pertinent strip: This is defined as a route that structurally and relationally shape the surroundings. The built area is the association of several identified built elements such as street, route, and embedded buildings [31].
3. The Built Route: The built routes are planned to provide connections between places as well as accessibility to construction sites. The city blocks are delineated by the well-connected routes since the connecting built routes can shape urban form [74].
4. The Block: The structure of a block is a basic structure of the urban pattern, and the block's geometric makeup is the defining factor of the form of the urban area. Kropf [81] pointed out that street dimensions depend on the length of a block.
5. Infill/Base Tissue: According to [74], this refers to the matrix route, described as an arrangement of particular parts and, such as the base type, also refers to a position in the typological process. Infill tissue is another term used in connection with the issue of the various types of urban tissue; it is the starting point from which a tissue evolves.
6. Node: A node is defined as any path crossing and a pole as the end/beginning of a path [74].

c.
Major (Macro-scale) refers to the 'urban organism', which is categorized into two elements: 1. The first is described as urban life, which refers to the totality of localized urban activities related to the functional structure of cities.
2. The second is distinct from the urban frame, which refers to the sum of spaces corresponding to the locality, concerning the functional and spatial urban structure [81].
Hence, the importance of combining scale hierarchy with a typo-morphology approach to delineate the content in the Minor scale and the meaning in the Major scale. Consequently, this combination will influence the accuracy of evaluating sustainability in the selected case study, according to the scale level ( Figure 8).

Integrated Synthesis and Formulating the Model
The first part of the theoretical framework of the study attempts to consider the global principles of SUF. Afterward, the authors, through literature (mainly Tadi et al. [42] and Manesh, et al. [58]), introduce the analytical tools of research for evaluating SUF. It was applied as an analytical process to reveal the relationship between morphological layers of a city and the design principles of SUF. In addition, the analysis has been carried out using urban morphology as a field of inquiry focusing on typo-morphology as an architectural and urbanism approach. Thereafter, the approach synthesizes in scale hierarchy based on Kropf's taxonomy [6] in order to develop spatially hierarchal structure as inputs data. Based on the above information, the model for evaluating the relationship between SUF and UM has been developed. The authors developed the model and considered the most valid indicators and the factors based on theoretical framework analysis. The model has been divided into three stages: 1. Input (Identification) stage: it includes the morphological classification based on the hierarchy concept, and scale of the case study, which is starting from town as Macro-scale and ending with building patterns as Micro-scale, sorting streets, and plot patterns as meso-scale. The model will focus on the architectural morphological approach, which is the typo-morphology approach, and it classifies the urban area into town, buildings, and systems organization. In this part, the input will involve the indicators of the urban form approaches sorted according to the concept of the scale commencing with the Micro-scale, followed by the middle-scale, and completing with the Macro-scale. Each of these scale stages has its characteristics to be tested through input data, such as materials, building types, and structures on the Micro-scale. Similarly, in respect of the meso-scale stage, which involves lots, pertinent strips, built routes, etc., and in the final Macro-scale stage, the characteristics will include urban organisms. These levels will be harmonized with the urban morphology classification framework, based on the scale. For example, 'The Approach of Buildings System', which is one of the urban morphology classifications that includes buildings' level details, will be involved in a Micro-scale or Minor level stage. The same process applies to other approaches; for example, the Approach of the Plots System, and the Approach of the Streets System will be involved in the meso-scale or middle-level stages. Whereas, again, the approach of the Streets System, the approach of the Urban Tissue stage, and the approach of the Natural Context will be involved at a Macro-scale or significant level stage.
2. The Analysis process (Evaluation) stage: this part will include the analysis of the input data considering interrelations with the principles of the SUF and the level of the relationships with the factors of the typo-morphology approach and their influences on or contribution to the achievement of the sustainability. All these factors are under the concept of the scale of the selected sample study. The absence, presence, or lack of contribution of the indicators in the first (Input) stage will be tested in this stage. The Analytical stage is demonstrated in Table 1 and Supplement Table S1; at this stage, the most weighted indicators will be evaluated according to their contribution, which depends significantly on the scale of the case study.
3. The output (Decision) stage: in this stage, all the previous principles and dimensions will be related to the global SUF as analytical tools. The validity of these factors will be tested in terms of their effects on the case studies. To examine the confidence and the validity of the suggested SUF, the analytical tools which are: intensity, proximity, efficiency, accessibility, diversity, and permeability will be applied to the case studies, based on the hierarchical scale of urban morphology which was explained in this study. Finally, the SUF types have been suggested for future studies to be evaluated based on these analytical tools and according to the three stages of the process of model development. Through these evaluations, the most effective SUF types will be evaluated ( Figure 9).

The Evaluation Processes of the Relationship between UM and SUF
The primary objective of the procedure is to concentrate on the evaluation of morphological principles in SUF, through testing the analytical tools of the latter. Referring to the analytical tools of SUF each of them should be combined with the hierarchical typomorphology approach, which is combined with the scale hierarchy (Figure 9), to test the validity of the contribution at five levels stated from strong contribution to non-contributed.
Consequently, the features of the relationship between UM (Typo-morphology approach) and the SUF (through analytical tools), have been recognized. This is by the amalgamation of all the discussions in this study classified, based on using the process of the typological approach in urban morphology, as shown in Table 1 and for more details see Supplement Table S1.

Methodology for Applying the Model
The description of the methodology will be implemented in this section to apply the proposed model for assessing the relationship between UM and SUF in urban contexts. To use the model, the following information is required: (1) The scale hierarchy of the study area (Micro, Meso, and Macro-scales).

Integrated Synthesis and Formulating the Model
The first part of the theoretical framework of the study attempts to consider the global principles of SUF. Afterward, the authors, through literature (mainly Tadi et al. [42] and Manesh, et al. [58]), introduce the analytical tools of research for evaluating SUF. It was applied as an analytical process to reveal the relationship between morphological layers of a city and the design principles of SUF. In addition, the analysis has been carried out using urban morphology as a field of inquiry focusing on typo-morphology as an architectural and urbanism approach. Thereafter, the approach synthesizes in scale hierarchy based on Kropf's taxonomy [6] in order to develop spatially hierarchal structure as inputs data. Based on the above information, the model for evaluating the relationship between SUF and UM has been developed. The authors developed the model and considered the most valid indicators and the factors based on theoretical framework analysis. The model has been divided into three stages: 1. Input (Identification) stage: it includes the morphological classification based on the hierarchy concept, and scale of the case study, which is starting from town as Macro-scale and ending with building patterns as Micro-scale, sorting streets, and plot patterns as meso-scale. The model will focus on the architectural morphological approach, which is the typo-morphology approach, and it classifies the urban area into town, buildings, and systems organization. In this part, the input will involve the indicators of the urban form approaches sorted according to the concept of the scale commencing with the Micro-scale, followed by the middle-scale, and completing with the Macro-scale. Each of these scale stages has its characteristics to be tested through input data, such as materials, building types, and structures on the Micro-scale. Similarly, in respect of the meso-scale stage, which involves lots, pertinent strips, built routes, etc., and in the final Macro-scale stage,

Mode of the Study
As already discussed, the main aim of the proposed model is to assess the relationship between UM and SUF to evaluate the level of sustainability in an urban context. As shown in Table 1, the evaluation is based on the contribution of each indicator to reach the level of sustainability in an urban area. Each of the indicators per resolution levels or scale (Micro, Meso, and Macro) will be weighted, based on its contributions, by using the analytical tools of the SUF. For example, in the 'Micro-Scale', building material has been contributed in three tools out of the six of the SUF analytical tools. This gives the indicator (3/6), which means a weighting of 50% in the contribution to the SUF. Rooms will not be evaluated in the model research because they are classified as internal factors. Moreover, for a more accurate evaluation, the weight of each indicator contribution can be classified into five levels with a specific number, for example, in 'Micro-Scale' of the typo-morphology's indicator, building material with intensity is contributed because of the mass or volume of construction materials per unit area provide a crucial measure of intensity. Accordingly, the level contribution of each spatially hierarchal structure is evaluated in terms of the analytical tools to achieve SUF based on the morphology of a city (for more details, see Supplement Table S1).

Mode of the Study
As already discussed, the main aim of the proposed model is to assess the relationship between UM and SUF to evaluate the level of sustainability in an urban context. As  (−2) Non-contributed (−1) Weak contribution (0) Neutral (1) Regular contribution (2) Strong contribution * Room will be not evaluated in the research.
The method which might be used for structuring questionnaires could be based on Likert's scale. Likert's scale is a method for obtaining the evaluation with five or seven response items [95]. In this study, Likert's scale used from 'strongly contributory' to 'non-contributory' categories ( Table 1). The difference in weighting depends on the scale hierarchy of an urban context.
The proposed model can be applied by planners and designers, within the context of their contribution, which relates to the scale of the selected case study. Additionally, the model offers an opportunity for planners to evaluate the context accurately.

The Applied Tools and Technique
To obtain reliable outcomes, a specific number of respondents, when considering the population of a selected context, should be found. Hence, Slovin's formula could be used to identify the sample size for such a study, with the margin of error of ±5% (n = N/(1 + Ne2) n = Number of samples-N = Total population-e = Error tolerance. The spatial hierarchy of the case study should be identified within the Macro, Meso, and Microscales. The indicators of each scale are determined, in Figure 10. Considering the selected context, the SPSS (statistical package for social science) can be applied to analyze the collected data statistically to obtain more accurate results, especially when there is a large amount of input data. The privilege of the SPSS computer tool is that the data can be entered by the researcher from different sources, but should be appropriately arranged. Moreover, entering the data will make the statistical calculation process an easy one, since only a few fundamental steps are required to be considered for obtaining accurate results. The outputs from Spearman's Correlation coefficient (r s ) are arranged between −1 and +1 [95,96]. Moreover, descriptive statistical methods can be considered for examining the collected data. The validity can be achieved using SPSS, whilst the reliability can be achieved through the use of Chronbach's Alpha test. The proposed methodology can be described as the Inventory Mapping Technique (IMT).
According to the proposed model, the morphological analysis based on the threescale of Micro, Meso, and Macro, demonstrated the effect of each level on sustainability, based on their specific elements within a morphological context. The model represents the interrelations between urban morphology and the principles of SUF. It suggests that global analytical tools are used as a guideline to test the SUF types based on urban morphology ( Figure 11).

Conclusions
The study developed the model to demonstrate the interrelations between sustainability and urban morphology. The relationship exists and would create a sufficient framework to support sustainable urban form based on morphological classification. This study strived to focus on typo-morphological approaches as the limitation of the study which contributed by integrating the approach based on Kropf's taxonomy (2017) to scale hierarchy. This interpretation is thus presented as a rigorous hierarchical structure in order to ease the complicated assessment. Additionally, the analytical keys are designated in the analysis stage to reveal the relationship between the two. Thereafter, the morphological analysis based on the three-scale hierarchy (Micro, Meso, and Macro) derived evaluate the effect of each level on sustainability, based on their elements within the morphological context. On the other hand, the indicators of the SUF relationship with the three main sustainable aspects have been confirmed, based on the interrelations between the indicators and the sustainability dimension indicators in urbanism. The model is taken as a guideline to test the SUF types towards analytical tools based on urban morphology. As aforementioned, this study has also revealed that the seven main factors for evaluating sustainability in the urban form are intensity, proximity, efficiency, accessibility, diversity, and permeability, which are the primary organizational factors for urban spatial configuration in terms of sustainability.
This study reveals that assessment in the field of urban design and an attempt to upsurge the quality of the urban environment in terms of sustainability is critical. In this sense, the study has been collected the principles as well as indicators of UM and SUF (projected on the concept of scale hierarchy), through reviewing the related literature and the classified framework based on an analytical process to demonstrate the relations between these indicators.
The outcome put forward is that the SUF is directly related to the urban morphological scale. The originality of this study will enhance the knowledge base linked to urban planning and design in respect of the role of urban morphology in sustainable urban planning. For future studies, the study recommends that the assessment of the sustainable urban form can be evaluated by conducting other approaches related to urban morphology rather than the one dealt with in this paper, i.e., Typo-morphology, e.g., the Historicogeographical, Spatial-analytical, or Configurational approach. Additionally, a model can be designed for the regional scale to raise geographical aspects.