Evaluating the sustainability performance of Turkish provinces with fuzzy logic

Sustainability is the balance of social, economic, and environmental factors. Evolving from history to the present, the goal of this concept is for humanity to live in harmony with nature. Sustainable development, on the other hand, encompasses achieving urban goals for the future while increasing prosperity and efficiently passing resources to future generations. Sustainability indicators are utilized to guide policymaking and monitor progress. Indicators introduced by various institutions vary by country. In developing economies like Turkey, which this study focuses on, there are a limited number of works on measuring sustainability performance. Hence, this study evaluates urban sustainability levels using the fuzzy logic method. Another objective is to develop a measurable and replicable numerical model to analyse the sustainability performance of cities in Turkey. The study employs a measurement set consisting of twenty-seven indicators from the main ecological, economic, and social components, and it assesses the sustainability levels of cities using fuzzy logic rules. Based on the results obtained, all eighty-one provinces of Turkey are classified into quantile groups and mapped. This analytical approach can guide urban planners, policymakers, and decision-makers. This study contributes to enhancing knowledge and understanding sustainability.


Introduction
In today's world, the e ects of COVID-19, population growth, climate change, environmental degradation, inadequate housing, and uncertainties related to the nexus of water, food, and energy are subjects of intense debate among academics, urban planners, and policymakers (Dumane et al., 2019;Son et al., 2023).e urbanization dynamic experienced since the Industrial Revolution has led to the rapid consumption of global resources by the human population.It is projected that by 2050 approximately 70% of the world's population, or 6.9 billion people, will live in cities (UNDP, 2020; Bharani & Ramesh, 2022).Ensuring the sustainability of life and cities and providing wellbeing for future generations require wise utilization of natural resources today.Alongside issues such as global warming, ozone layer depletion, housing, health, and the environment, policymakers need to strive for sustainable development in cities (Dumane et al., 2019).
Sustainability can be thought of as the fundamental goal of people living in harmony with nature (Robati & Rezaei, 2022).Sustainability, in a general sense, involves striking an appropriate balance among social, economic, and environmental factors (Dumane et al., 2019).e concept of sustainability has evolved from the past to the present with increasing inclusivity and continuous development.Etymologically, it comes from Latin sustinere 'to stand, endure' (Alptekin & Saraç, 2017).Sustainability is a long-term concept (Kusakci et al., 2022).It holds signi cant implications for both the private and public sectors.For businesses, it signi es adaptability to the competitive market and gaining a competitive advantage, whereas in the public sector it serves objectives such as cost e ciency, positive environmental outputs, directing the private sector toward sustainable technologies, and fostering consumer awareness about environmental and ecological issues (Akçakaya, 2016).
Sustainable development is de ned as sustainable economic growth and ecological renewal.e concept of sustainable development has been pushed to the forefront of urban policy debates with the hope of constructing a desirable urban future It promises to achieve urban goals without compromising the welfare of society, quality of life, and the environment (Son et al., 2023).Sustainable development indicators are used as a source of information for cra ing strategic documents and development programs.ey aid in setting priorities, monitoring the success of solutions to problems, and gauging the success or failure of interventions related to environmental, social, and economic issues.e aim is to integrate the public into the decision-making process by designing, selecting, and evaluating indicators collaboratively (Michalina et al., 2021).Indicators provide information to the public, researchers, and policymakers.
One method that can be employed to measure the sustainability performance of cities is the fuzzy logic method.Fuzzy logic converts expressions conveyed in natural language into mathematical concepts, and it constructs a logical structure tailored to a speci c problem (Robati & Rezaei, 2022). is structure reduces uncertainty and complexity within the system and provides clearer results.e fuzzy logic method allows for the representation of a city's sustainability level not in sharp terms such as good or bad, but in degrees of goodness or badness.e hypothesis of this study is " e fuzzy logic method can serve as an e ective tool for evaluating the sustainability levels of cities using a measurement set encompassing various sustainability components and indicators." is hypothesis is based on the ability to categorize cities in Turkey according to their sustainability performance levels into quartile groups using the fuzzy logic method.e aim of the study is to make sustainability performance measurable with a model that is applicable, repeatable, and based on numerical data.e measurement set developed for this study to measure the sustainability performance of cities is approached with the fuzzy logic method.e results obtained have the potential to serve as a guide for city planners, policymakers, and decision-makers to create more sustainable cities. e study starts by providing background information from the literature, followed by information about the sustainability of cities in Turkey and fuzzy logic.en, the method section explains the model created for this study.Finally, the ndings are presented and evaluations are made.

The concept of the sustainable city and monitoring the sustainability of cities
In today's context of creating a sustainable world, it is of great importance to manage cities, which have local and global impacts on natural resources and ecological balance, as well as changes and transformations in these cities.Referred to as "urban sustainability" or the "sustainable city", the integrated development of cities with economic, social, and environmental sensitivities entails signi cant responsibilities for local governments, which are the closest public institutions to urban communities.e functions of local governments are manifested in areas such as producing urban sustainable policies and measuring urban sustainability performance (Akçakaya, 2016).Urban sustainability can be considered the part of sustainable development that emphasizes the balance between environmental, economic, and social sustainability, highlighting the improvement of human wellbeing and quality of life (Robati & Rezaei, 2022).On the other hand, the international organization ICLEI (Local Governments for Sustainability) states that "sustainable cities work towards providing environmentally, socially, and economically healthy and exible living conditions for current populations, without compromising the ability of future generations to have the same experience" (Figure 1).However, many issues in cities require responsible institutions to address and ideally resolve them (Michalina et al., 2021).
e concept of urban sustainability was addressed during the United Nations Habitat II Conference on Human Settlements, also known as the City Summit, held in Istanbul in 1996 (Alptekin & Saraç, 2017). is concept emerged from the idea that cities need to carefully and e ectively utilize natural resources to meet the needs of current and future generations, as well as to inclusively support people.Sustainable cities are characterized by environmental sustainability measures such as conserving the environment, energy and water e ciency, reducing carbon footprints, preserving green spaces, and implementing recycling and waste management (Pınarcıoğlu & Kanbak, 2020).Economic sustainability implies that cities should promote economic growth while increasing job opportunities, reducing inequalities, and preventing poverty.Social sustainability, on the other hand, means that all communities living in cities have equal opportunities, accessible transportation, and easy access to education, health, housing, and other essential services (Figure 2).Furthermore, preserving cultural diversity, enhancing community participation, and strengthening democratic processes are also important for social sustainability (Michalina et al., 2021).
e Sustainable Development Goals (SDGs) consist of seventeen goals and 169 targets adopted by the United Nations in 2015 with the aim of promoting sustainable development globally by 2030 (UN, 2015).ese goals aspire to build a more sustainable and equitable world, addressing both urban and rural areas.e Sustainable Development Goals, which seek to complete what the Millennium Development Goals could not achieve, prioritize the balance between the three  dimensions of sustainable development: economic, social, and environmental.Urban sustainability holds a signi cant place within the Sustainable Development Goals.For global development, it is imperative that the majority of the population living in cities also become sustainable.For example, the goal Clean Water and Sanitation (SDG 6) comprises targets related to sustainable water resource utilization, clean water provision, and wastewater disposal within urban areas.Sustainable Cities and Communities (SDG 11) is a goal directly related to urban sustainability.It expects factors such as sustainable infrastructure, transportation systems, energy usage, and urban planning to contribute to the liveability and sustainability of cities. Clean Energy (SDG 7) is a goal that encourages the promotion of renewable energy in urban areas.Good Jobs and Economic Growth (SDG 8) aim for sustainable and inclusive growth.It describes the economic role that cities need to assume, such as job creation and promoting economic growth.Health and Wellbeing (SDG 3) is greatly impacted by urban planning.A clean environment, green spaces, and well-planned cities can contribute to people living healthier lives.Reducing Inequalities (SDG 10) is signi cant for social sustainability in cities. Decreasing inequalities in areas such as income, education, and living standards within urban areas is a key target.
Sustainable urbanization is considered one of the key elements of sustainable growth.erefore, measuring the sustainability of cities and evaluating their performance are thought to be responses to achieving growth goals.As a result, urban sustainability indicators, designed as a framework comprising environmental, economic, and social aspects, are used as tools to assess the sustainability performance of cities (Pınarcıoğlu & Kanbak, 2020).Monitoring sustainable urban development poses a challenge for policymakers in terms of selecting relevant thematic categories and indicators.e selection of categories and indicators is carried out based on meeting speci c criteria and requirements.e entire process of selecting categories and indicators must be transparent, methodologically accurate, and clearly justi ed.In most cases, eliminating the subjective nature of this process is di cult because the selection of categories and indicators is not value-neutral; rather, it re ects the biases, failures, intentions, assumptions, and worldviews of the framers of the framework (Michalina et al., 2021).
e European Commission's 2018 report Indicators for Sustainable Cities discusses the function of performance indicators in measuring sustainability performance.In this context, urban sustainability indicators can provide urban planners, local administrators, and policymakers with the ability to measure the socioeconomic and environmental performance of the city.Urban sustainability indicators that assist in measuring the city's performance in areas such as urban design, infrastructure services, policies, waste disposal systems, pollution, and accessibility to services not only aid in identifying issues but also help identify areas of improvement through good governance and research (Akçakaya, 2016;European Commission, 2018).Due to the signi cant variations in terms of available resources, population size, and urban metabolic processes among cities, the richness of sustainability indicators is bene cial.However, selecting appropriate sustainability indicators can be challenging (European Commission, 2018).
ere are measurable and comprehensible economic, social, and environmental indicators that allow for comparisons between di erent geographical regions and times to determine whether sustainable development is taking place in cities and to what extent (Çolakoğlu, 2019).Sustainability indicators are a proven method to promote sustainable urban development, and there are hundreds of di erent sets and frameworks available.e United Nations Human Settlements Programme (UN-Habitat), the UN Sustainable Cities Program, the World Bank's City Strength Diagnostic, the Sustainability Index for Cities, and the European Sustainable Cities Award have all introduced various indicators to measure the sustainability of cities (European Commission, 2018).Urban sustainability indices allow city planners and policymakers to assess the economic, social, and environmental impacts of applied urban plans on infrastructure development, policies, pollution, and citizens' access to services (Robati & Rezaei, 2022).Generally, there is no clear consensus on the methodology or standards in indicator sets that de ne the fundamental elements a city needs to ensure its sustainability (Pires et al., 2014).

Sustainability of cities in Turkey
ere are a considerable number of studies on the sustainability performance of cities in developed countries, but there are relatively few studies focusing on emerging economies such as Turkey, mainly due to the incipient stage of the indicator-based approach (Kusakci et al., 2022).Cities in Turkey, which have experienced signi cant urban growth in the past y years, are home to approximately 75% of the total population.Cities in Turkey face diverse environmental and social challenges that require a variety of sustainable measures.According to Turkey's Tenth Development Plan, the most critical urban issues are inadequate housing units, tra c congestion, security and infrastructure de ciencies, social cohesion, migration, and environmental degradation (Kusakci et al., 2022).Moreover, the World Bank Group has supported sustainable development in Turkey through the Sustainable Cities Project by expanding nancing.e program aims to improve the economic, environmental, and social sustainability of cities by enabling municipalities to access funds for priority investments (World Bank, 2019).Unfortunately, a shared set of sustainability measurement indicators for all provinces in Turkey is not yet available.
Evaluating the sustainability performance of Turkish provinces with fuzzy logic As a member of the United Nations, Turkey also signed the Paris Agreement in 2021, indicating its increased e orts in addressing climate change.When examining the studies conducted on the sustainability of cities in Turkey up to this point, it is evident that various analysis methods have been used.Gülcan and Aldemir (2008) compared two provinces in the Aegean Region (Aydın and Denizli) in terms of economic and sociocultural factors.ey stated that economic factors alone are not su cient to evaluate sustainability.erefore, other factors such as cities' cultural values and networks must also be included (Kusakci et al., 2022).e Sustainability Study of Turkey's Cities, conducted in 2011 in collaboration between Boğaziçi University and MasterCard, was examined.is study used both objective and subjective data.Objective data involved using indicators published at the province level to calculate sustainability and quality of life indices covering all eightyone provinces in Turkey.In addition to objective assessment, a survey was conducted with business managers in twenty-nine provinces, including twenty-six regions at the NUTS 2 level and sixteen metropolitan municipalities for subjective evaluation (MasterCard Worldwide & Boğaziçi Üniversitesi, 2011).Gazibey et al. (2014) analysed the sustainability performance of the eighty-one provinces in Turkey using social, economic, and environmental indicators and the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method.e TOPSIS method is a technique for determining the preference ranking of alternatives in multi-criteria decision problems (Hwang & Yoon, 1981).e TOPSIS method aims to simultaneously identify alternatives that are closest to the "positive ideal solution" and farthest from the "negative ideal solution".
e positive ideal point has the highest bene t and the lowest cost, and the negative ideal point is associated with the lowest bene t and the highest cost.Consequently, the ranking of alternatives is established in descending order based on their relative proximity values to the ideal solutions (Gazibey et al., 2014).e results indicated that Kocaeli, Istanbul, and Ankara were the top three sustainable cities.It was emphasized that the results from this study could assist in making decisions during the creation of new public policies and help achieve a balance between costs and bene ts among stakeholders.e need for new indicators and the necessity of data collection related to these new indicators for evaluating the sustainability of provinces in the country were highlighted (Alptekin & Saraç, 2017).Yıldırım et al. (2017) focused on examining the perception levels of local government personnel in Istanbul regarding environmental sustainability tools by evaluating indicators of Local Agenda 21, including social activities, renewable energy projects, energy e ciency projects, green transportation, and waste management.e results indicated that strategy-based practices such as sustainable planning and participatory policies were more successful than project-based applications (Kusakci et al., 2022).Alptekin and Saraç (2017) used the entropy weight determination method for determining the importance levels (or weights) of each variable in the indicator set that assists in measuring sustainable development.ey also employed the grey relational analysis technique, a multi-criteria decision-making method, to establish rankings for sustainable development among provinces in Turkey (Alptekin & Saraç, 2017).Finally, in their study conducted in 2022, Kuşakçı et al. used the IT2D-AHP method to reveal that the level of urban sustainability in the thirty metropolitan cities in Turkey varied in economic, social, environmental, and institutional dimensions through the Sustainable Cities Index (Kusakci et al., 2022).e aim of all these studies is to raise awareness about urban sustainability, provide data-based contributions to policymakers' decision-making processes, and o er a roadmap for measuring and improving the performance of cities in terms of sustainability.
De ning urban sustainable development in purely quantitative terms is di cult, and over the past decades researchers have acknowledged the inherently uncertain and ambiguous nature of de ning and addressing indicators related to the e cient and e ective use of resources through various data collection methods (Hincu, 2011).e outcomes of sustainable development are uncertain in both qualitative and mathematical sustainability assessments.To obtain a sustainable model for a city system, the sustainability of subsystems can be integrated using fuzzy logic (Jaderi et al., 2014).Sustainable development is a concept that simultaneously meets the needs of economic, social, and environmental dimensions.Andriantiatsaholiniaina et al. (2004) developed the SAFE (Sustainability Assessment by Fuzzy Evaluation) model, which can be explained by fuzzy logic and uses basic, environmental integrity, economic e ciency, and social solidarity indicators to measure sustainable development.ey proposed this model for the Greek and American economies and argued that there is no single way to make e ective sustainable decisions, advocating the use of di erent indicators for each country (Alptekin & Saraç, 2017).

Fuzzy logic
Fuzzy logic is a method that was introduced by Lot A. Zadeh in 1965.Fuzzy logic is a mathematical approach used to model and control systems that involve uncertainty, lack of precise boundaries, or transitions between speci c values (Robati & Rezaei, 2022). is method is designed to handle uncertainties commonly encountered in complex and real-world scenarios.Fuzzy logic aims to equip machines with the ability to think and make conclusions like humans, using imprecise terms expressed in natural language (Phillis et al., 2017).e E. ÖZMEN, F. YİRMİBEŞOĞLU applications of fuzzy logic are quite extensive, including control systems, arti cial intelligence, robotics, image processing, machine learning, natural language processing, economics and nance, and environmental and energy management.In addition, fuzzy logic is used in various sectors such as healthcare, tra c management, industrial processes, and agriculture.Fuzzy methodologies can address assessment challenges in sustainability evaluations.As an appropriate method, in urban sustainability analysis, it is o en used for purposes such as developing composite indices to rank and assess urban sustainability performances, evaluating urban renewal projects, and comparing local-scale units or cities from around the world (Buzási et al., 2022).
Unlike traditional binary logic, fuzzy logic evaluates the innite possibility range within the interval (0-1) because it does not have strict binary thresholds.Fuzzy logic can be employed as a method to model and analyse uncertain and complex systems (Hincu, 2011). is method helps reduce uncertainty in the data, aiding in better understanding the system.e method also allows for the incorporation of expert opinions and experiences.e fuzzy logic method describes a process in which numerical data are rst evaluated verbally and then expressed numerically again at the output.e fuzzy logic process is summarized in Figure 3. e method starts with the fuzzi cation process, in which numerical data are transformed into verbal expressions.For each input datum, membership functions are created in various shapes such as triangles, Gaussian curves, or trapezoids.ese membership functions are de ned using verbal expressions such as low, medium, and high.e second stage of the method is called the fuzzy decision-making process, in which the output expression is de ned based on the relationship between membership functions.e rules in this stage are expressed as "if . . .and/ or . . .then . .." rules.In this way, a verbal output is obtained based on the relationship between di erent inputs.In the nal stage of the method, the numerical counterpart of the verbal output expression obtained is calculated, and this stage is referred to as defuzzi cation (Figure 3).

Method
is study employs the fuzzy logic method within a model based on an indicator set to monitor the sustainability performance of all cities in Turkey.e sustainability performance of a city is addressed based on numerical data along with sub-components de ned within the main ecological, economic, and social components.e ecological component includes subcomponents of air, water, soil, and energy.Two indicators are used for air, two for water, three for soil, and two for energy.e economic component includes subcomponents of work life and livelihood, with three indicators used for each.For the social component, the subcomponents are de ned as population, education, health, and housing.Population is examined through two indicators, education through four, health through three, and housing through three.e results were obtained for the main components by applying fuzzy logic rules to the indicators.By applying these fuzzy logic rules again to the data obtained, the sustainability levels of all cities in Turkey were calculated individually.
In this study, careful attention has been given to whether each selected indicator for determining the sustainability performance of provinces has a counterpart at the provincial level.
e indicators utilized in the study have also been employed in previous research related to this subject in Turkey.Detailed explanations regarding the data, the reference study for the data, and the impact of the fuzzy logic rules (positive/negative) are provided in Table 1.e limitations of this study include accessing data at the provincial level and selecting the same or the nearest available year as the reference year.Although data in Turkey are recorded by the Turkish Statistical Institute (TSI, 2020(TSI, , 2021(TSI, , 2022)), some data were obtained from other sources.Data related to commercial establishments were obtained from the Union of Chambers and Commodity Exchanges of Turkey (UCCE, 2022), housing depreciation data from the Endeksa website (Endeksa, 2022), forest assets from the General Directorate of Forestry ( 2021), and electricity-related data from the Energy Market Regulatory Authority (EMRA, 2022).Evaluating the sustainability performance of Turkish provinces with fuzzy logic E. ÖZMEN, F. YİRMİBEŞOĞLU e data have been normalized within their value ranges and scaled to a range of 0 to 1. Normalization has been applied to the data in the study because the indicators are expressed in di erent measurement units.is ensures that cities can be compared.e normalization process has been performed based on the minimum and maximum values in the data sets related to the indicators, using the following formula: where x norm is the normalized value, x is the real value, x min is the minimum value, and x max is the maximum value in the data set. is model starts from the indicators and ultimately reaches the sustainability performance degree.All membership functions have been chosen in the form of a triangle due to their convenience and frequent preference in the literature (Figure 4).Membership functions at all stages have been uniformly and evenly distributed.In the rst stage of the model, membership functions for the indicators have been de ned as Low (L), Medium (M), and High (H) in triplets.e boundary values used to create these triangles are provided in the table as P1, P2, and P3. e basic indicator, sub-component, component, and sustainability limits in the study are given in Figure 4.
Rules were written for the relationships between indicators and sub-components.In writing these rules, all components were treated with equal weight in line with expert opinions.
e positive e ects of some components and negative e ects of others were considered in writing the rules.By running the MATLAB program, data in the range of 0 to 1 for sub-components were obtained.In the second stage, triplet membership functions were created for sub-components using Low (L), Medium (M), and High (H) expressions based on the data related to sub-components.Rules were written for the relationships between sub-components and components.By running the MATLAB program, results in the range of 0 to 1 for components were obtained.In the nal stage, membership functions for components were created as Low (L), Medium (M), and High (H) expressions in triplets.Rules were written for the relationships between components and sustainability, and the sustainability performance values were obtained in the range of 0 to 1 as a result of the model (Figure 5).
In this study, the Mamdani fuzzy inference method was applied.e Mamdani method consists of four stages: fuzzication of input variables, evaluation of rules, aggregation of rule outputs, and defuzzi cation.In the fuzzi cation stage, numerical values of the inputs are associated with membership degrees in their corresponding membership functions.
e evaluation of rules determines the output based on the membership degrees of the inputs, nding the corresponding output function values.e values of the inputs are applied to all written rules, and the output functions are aggregated.Evaluating the sustainability performance of Turkish provinces with fuzzy logic e COG (centre of gravity) formula represents the centroid of the output fuzzy set.μ (x) denotes the membership degree, and x represents the value of this membership degree in the output function.Using these values, the centroid is calculated within the boundaries of a and b, providing the numerical value of the output function.e MATLAB Fuzzy Toolbox interface for calculating sustainability values is provided in Figure 6.Numerical data related to the ecological, economic, and social components of the city for which the calculation will be performed intersect with the membership functions in the rules.ese values correspond to fuzzy sets obtained in the sustainability output.is process is applied to all rules, and all sustainability output sets are aggregated.e centroid of the aggregated set is calculated, and the sustainability index for that city is computed.

Results
e results obtained for each of the eighty-one provinces in Turkey were divided into ve quantile (twenty-percentile) groups.e cities were ranked as follows: sixteen cities in  is stage involves the summation of all rule outputs.e nal stage, defuzzi cation, expresses the obtained fuzzy set result as a single number.For this purpose, the centroid technique was used.In the centroid technique, the centre of gravity of the output fuzzy set is calculated.e formula used for this is: the rst group, sixteen in the second group, seventeen in the third group, sixteen in the fourth group, and sixteen in the last group.e cities, sorted from the lowest to the highest degree, were mapped.e outputs obtained from the ecological, economic, and societal main components of the cities grouped according to sustainability performance were also classi ed and mapped using the same system.e most populous cities in Turkey (Istanbul, Ankara, and Izmir) were evaluated under each main component.

Ecological main component
Within the ecological main component, nine di erent indicators were evaluated within four sub-components.According to the evaluation results, the province with the lowest ecological performance level, in the rst group, is Malatya.A er Malatya, the provinces with the lowest performance are Hakkari, Batman, Hatay, and Burdur.e province with the highest performance in the last group is Karaman.e Erzurum, Sakarya
Evaluating the sustainability performance of Turkish provinces with fuzzy logic Gaziantep, and Ankara provinces reached the highest values a er Karaman.Table 2 shows the distribution of performance values for all cities and the groups they belong to.In terms of ecological performance, the Ankara province has a higher value compared to Istanbul and Izmir.Istanbul is in the second group and Izmir is in the third group, whereas Ankara is in the best group, which is the h group.

Economic main component
e economic main component consists of two sub-components and a total of six indicators.e values obtained in the economic component were lower than the values observed in all other main components.Mard n had the lowest economic performance, and Bursa showed the highest performance.Izmir is in the th rd group, and Ankara and Istanbul are in the fourth group.Table 3 shows that the Aegean region and the Southeast Anatolia region stand out economically.

Social main component
e social main component has more indicators than the economic and ecological components.Within the social component, consisting of a total of twelve indicators, there are four sub-components.As a result of the evaluation, it can be seen that the Sinop province has the lowest performance.e Ağrı, Şanlıurfa, Afyonkarahisar, and Gaziantep provinces have the lowest performance a er Sinop.e province with the highest performance is Istanbul.Antalya, Aydın, Ankara, and Artvin are other provinces in this group.e Izmir, Ankara, and Istanbul provinces are all in the highest level, which is the h group.Table 4 shows the results of the social main component.

Sustainability performance
When the results of the sustainability performance ratings are evaluated based on the 2022 data, it is observed that Bilecik, Malatya, Bursa, Burdur, and Uşak are the lowest-ranking provinces.e provinces showing the highest sustainability performance are Erzurum, Karaman, Kahramanmaraş, Osmaniye, Sivas, and Istanbul (Table 5).With di erentiation in each region, higher sustainability performance in cities located in the middle of Turkey is evident.According to the analysis results, there are signi cant di erences in sustainability levels among provinces.

Discussion
is study was conducted using a fuzzy model with the aim of assessing the sustainability performance of cities in Turkey.
is model takes into account three main components -namely, the economy, ecology, and society -and encompasses a total of twenty-seven indicators.Based on the research ndings, it is observed that di erent cities in Turkey exhibit varying levels of sustainability performance.When comparing the results of this study to those of previous research, various di erences and similarities are observed.
e study conducted by MasterCard (2011) utilized sixty-nine indicators under the categories of economic, social, and environmental components, and it demonstrated that the western regions of Turkey are more sustainable, whereas the eastern and southeastern regions are less sustainable.Another study by Gazibey et al. (2014) employed a total of y-two indicators and identi ed Kocaeli, Istanbul, Ankara, Izmir, and Canak-kale as the most sustainable cities, while ranking Adiyaman, Mardin, Sanliurfa, Kilis, and Hakkari as less sustainable.ese results support the thesis that western Turkey is more sustainable and the southeastern regions less so.A study by Alptekin and Saraç (2017) examined y-one indicators under the categories of economic, social, and environmental components.According to data from 2013, they ranked Istanbul, Ankara, Antalya, Kocaeli, and Izmir as the most sustainable cities and identi ed Kilis, Duzce, Sinop, Bartin, and Kastamonu as less sustainable.ese results also indicate that western Turkey is more sustainable, with cities in the Black Sea and Southeast Anatolia regions being less sustainable.
Finally, a study by Kusakci et al. ( 2022) considered y-three indicators under the categories of economic, environmental, social, and institutional components, but only examined three major cities.In this study, they designated Antalya, Mugla, Eskisehir, Ankara, and Kocaeli as the most sustainable cities while ranking Van, Mardin, Ordu, Diyarbakir, and Sanliurfa as less sustainable.Similar to other studies, this study found that the sustainability performance in the southeastern provinces of Turkey is lower, but, uniquely, it observed that the central Anatolian and Mediterranean regions of Turkey exhibited higher sustainability performance, possibly due to di erences in the model framework, the methodology, and the pandemic e ects speci c to the year when the data were collected (Figure 7).
In all the studies conducted on the sustainability of cities in Turkey, it is observed that the cities with the highest population -namely, Istanbul, the capital Ankara, and Izmir -are evaluated among themselves.When the sustainability performance of these cities is assessed using the model employed in this study, the ranking is as follows: Istanbul, Ankara, and Izmir. is result is consistent with similar studies in the literature, in which cities with higher populations, typically large metropolitan areas, tend to exhibit higher sustainability performance compared to smaller cities. e results obtained in this study indicate that smaller cities can compete with larger cities in terms of sustainability performance, emphasizing the need to harness the potential of smaller settlements in terms of sustainability.For instance, in this study, the Erzurum province emerged as having the highest sustainability performance, which can be attributed to the rule-based and exible nature of the fuzzy logic method.However, it is important to note that this study, like others, has certain limitations.One limitation is that the data used are speci c to a particular period.In addition, the use of equal weights for indicators and their selection represents other limitations.Future studies could examine the e ects of using di erent indicators and adjusting the weights of indicators.
Evaluating the sustainability performance of Turkish provinces with fuzzy logic

Conclusion
Cities have been important centres for the social, economic, and cultural development of humanity throughout history.However, with the increasing pace of urbanization, population growth, and environmental impacts, the concept of sustainability has become a signi cant issue for cities.Sustainable cities combine planning, management, and technological perspectives to ensure long-term liveability and wellbeing from environmental, economic, and social perspectives.ese cities work toward achieving sustainability goals to create a healthy and liveable environment for future generations.Policymakers, local governments, urban planners, and academics today face a wide variety of existing sustainability indicator frameworks.
is study measured the sustainability performances of cities in Turkey through the application of the fuzzy logic method, considering economic, ecological, and social components.e cities were divided into quantiles (twenty-percentile) groups based on their achieved sustainability levels.e performance results will serve as a guide for identifying areas where more work needs to be done in terms of speci c sustainability components in cities. e fuzzy logic method has been shown to be an important analytical tool in the eld of sustainability due to its ability to address uncertainties and complexities.It is believed that this model will provide urban planners, policymakers, and decision-makers with better opportunities to develop strategies and policies for creating more sustainable and liveable cities. is model, which is repeatable, adaptable, and allows for comparisons based on numerical results, is expected to contribute to the literature.Future studies will repeat this model for data from di erent years, compare the results, and observe changes in cities' sustainability levels over time.
Ece Özmen, Istanbul Technical University, ITU Graduate School, Department of Urban and Regional Planning, Maslak -Istanbul, Turkey E-mail: simsekec@itu.edu.trFunda Yirmibeşoğlu, Istanbul Technical University, Faculty of Architecture, Department of Urban and Regional Planning, ITU Faculty of Architecture, Department of Urban and Regional Planning, Şişli -Istanbul, Turkey E-mail: funday@itu.edu.tr

Table 1 :
Sustainability performance model indicators.