Designing an Integrated SMART Indicator Framework for Urban Green Transitions: Aligning SDGs and ISO 37120 at City Level

Abstract

Urban areas are pivotal to achieving the Sustainable Development Goals (SDGs), yet sustainability monitoring at the municipal level remains fragmented, difficult to operationalize, and weakly comparable across cities. Although the SDGs provide a comprehensive global agenda and ISO 37120 offers a standardized set of city indicators, municipalities still face practical barriers in translating global targets into actionable, jurisdiction-sensitive, and measurable metrics aligned with local responsibilities and available data. This study addresses this gap by presenting the design of an integrated, target-level urban sustainability assessment framework grounded in SMART (Specific, Measurable, Achievable, Relevant, and Time-bound) principles and explicitly tailored to municipalities in developed-country contexts. The framework contributes (i) a structured procedure for disaggregating and reallocating SDG targets according to municipal responsibilities, (ii) a six-dimension architecture that consolidates SDG targets and ISO 37120 themes into a coherent, governance-oriented structure (Government and Economic Development; Civic & Social Infrastructure; Environment and Climate; Infrastructure and Urban Planning; Health; Urban Living Conditions), and (iii) a SMART-based indicator screening logic that prioritizes feasibility, data availability, and benchmarking potential, thus supporting the green transition in Urban Areas. The framework is empirically examined through validation against sustainability reporting practices of the Porto City Council, quantifying indicator coverage, assessing alignment with municipal mandates, and identifying systematic gaps—particularly in cross-cutting areas such as governance transparency, equity monitoring, and long-term climate adaptation. Overall, the results indicate that the proposed approach strengthens coherence, measurability, and comparability in urban sustainability assessment, supporting evidence-based municipal decision-making, performance benchmarking, and more strategically aligned SDG localization.

1. Introduction

Urbanization remains a defining trend of the twenty-first century. More than half of the global population now resides in urban areas, and projections suggest that this figure may approach 70% by 2050 [1]. Cities act as central hubs of economic activity, innovation, and social interaction, generating a substantial share of global wealth and employment [2]. At the same time, they account for a disproportionate share of environmental pressures, including energy consumption, greenhouse gas emissions, waste generation, and ecosystem degradation [3,4]. Consequently, the concentration of both opportunities and impacts within cities has intensified concerns regarding the long-term sustainability and resilience of urban systems. Rapid urban growth has amplified challenges related to social inequality, access to essential services, housing affordability, environmental quality, and climate vulnerability [5,6]. In response to these interlinked challenges, the concept of urban sustainability has gained prominence, commonly defined as the capacity of cities to achieve economic vitality, social equity, and environmental protection while maintaining resilience to internal and external shocks [7,8].

Against this backdrop, the adoption of the 2030 Agenda for Sustainable Development by the United Nations in 2015 marked a major milestone in global sustainability governance. The agenda introduced 17 Sustainable Development Goals (SDGs) and 169 associated targets as a universal framework to guide development efforts worldwide [9]. Unlike earlier international frameworks, the SDGs apply to all countries regardless of income level and explicitly emphasize the interdependence among social, economic, environmental, and institutional dimensions of sustainability [10]. Within this framework, cities occupy a particularly central position. One SDG is explicitly dedicated to sustainable cities and communities, while many others depend indirectly on effective urban action. Empirical evidence suggests that approximately 65% of SDG targets cannot be achieved without implementation at the local and municipal levels [11,12]. As a result, local governments are increasingly recognized as key actors in translating global sustainability ambitions into concrete actions [13].

Despite this growing prominence, municipalities face structural barriers in adopting the SDGs as practical policy tools. The goals were not originally conceived as an operational framework for local authorities. Their global scope and broad, often abstract targets complicate integration into municipal policy planning, implementation, and monitoring processes [14,15]. These challenges have intensified calls for the localization of the SDGs—namely, the adaptation of global goals and targets to local contexts, priorities, and governance structures [16]. However, localization efforts frequently encounter operational frictions. Many SDG targets and indicators fall outside municipal jurisdiction, relying instead on national or regional policies, which limit local accountability and actionability. Moreover, numerous global SDG indicators lack the spatial resolution required for city-level monitoring or depend on data that are unavailable, infrequently updated, or methodologically inconsistent across municipalities. At the same time, cities face fragmented reporting requirements—combining SDG monitoring, standardized indicator systems, and local sustainability strategies—which increase administrative burden while undermining strategic coherence.

These frictions often result in sustainability monitoring systems that are more symbolic than operational, offering limited support for prioritization, benchmarking, or evidence-based decision-making at the municipal level. This situation highlights the need for assessment frameworks that explicitly reflect municipal responsibilities, align indicators with reliable and accessible data sources, and remain consistent with global sustainability agendas.

Within this study, the concept of urban green transition refers to the gradual transformation of urban governance systems toward environmentally sustainable, socially inclusive, and economically resilient development pathways. In practical terms, such transitions require the capacity to monitor progress through clear and measurable indicators. Consequently, indicator definition, monitoring, and systematic follow-up represent a critical first step in enabling urban green transitions, as municipal authorities require reliable metrics to evaluate sustainability performance and guide policy adjustments.

One of the most persistent challenges in localizing the SDGs concerns the selection and use of appropriate indicators. Although the global SDG indicator framework is comprehensive, it frequently lacks the spatial resolution, data availability, and institutional alignment required for effective municipal decision-making [17,18]. Conversely, locally developed indicators often suffer from limited standardization, weak methodological rigor, and reduced comparability across cities [19,20]. To address these limitations, several international organizations have developed standardized indicator frameworks for urban sustainability assessment. Among these, ISO 37120 [19] has gained prominence as an international standard for measuring city services and quality of life through a structured and comparable set of indicators [21]. The standard enables cities to benchmark performance over time and across contexts, covering economic, social, and environmental dimensions [22]. However, the application of ISO 37120 in isolation does not fully resolve the challenge of aligning urban sustainability monitoring with the SDGs. The standard does not explicitly map its indicators to SDG targets, nor does it systematically address the division of responsibilities across levels of government [22,23]. Consequently, municipalities often continue to face fragmented reporting systems, duplicated efforts, and weak integration between sustainability strategies and performance measurement.

Accordingly, the literature reveals a clear gap in integrated approaches that combine global sustainability frameworks with standardized urban indicators while remaining grounded in municipal realities. In particular, the novelty of this study lies in the integration of SDG targets, ISO 37120 indicators, and SMART principles within a governance-oriented framework explicitly aligned with municipal responsibilities. While previous studies have addressed these elements individually, the proposed framework combines them into a coherent structure designed to support operational sustainability monitoring and decision-making at the municipal level. Specifically, there is a lack of models that align SDG targets with municipal responsibilities, apply SMART principles to ensure operational relevance, and preserve comparability across cities and contexts [18,24]. This study seeks to address this gap by developing an integrated SMART indicator framework for urban sustainability assessment. The framework is designed to support municipalities in operationalizing sustainability by translating global SDG targets into context-sensitive indicators aligned with municipal accountability and supported by reliable data sources. By reorganizing SDG targets and ISO 37120 indicators into a coherent structure reflecting core dimensions of urban sustainability, this study contributes to more effective sustainability monitoring, benchmarking, and evidence-based decision-making at the local level.

The remainder of this paper is structured as follows. Section 2 outlines the research design and methodological approach, including the literature review process, framework development, indicator selection criteria, and validation strategy. Section 3 presents the main findings, describing the framework structure, the alignment between SDG targets and ISO 37120 indicators, and the results of the municipal case validation. Section 4 discusses the theoretical and practical implications of the findings within the broader urban sustainability literature. Finally, Section 5 concludes by summarizing the main contributions and outlining directions for future research.

2. Materials and Methods

2.1. Research Design and Methodological Overview

This study adopts a qualitative and analytical research design aimed at developing and validating an operational framework for urban sustainability assessment at the municipal level. Rather than pursuing a hypothesis-testing or model-estimation approach, the study focuses on conceptual integration, indicator structuring, and empirical applicability. This design choice reflects the multidimensional, governance-driven, and context-dependent nature of urban sustainability, which requires both analytical synthesis and practical feasibility [25,26].

The methodological approach is structured around four interconnected stages. First, a targeted and structured review of the scientific literature was conducted to identify dominant approaches to urban sustainability assessment, common challenges in SDG implementation at the local level, and prevailing practices in indicator design and use. Second, an integrated conceptual framework was developed by reorganizing SDG targets and ISO 37120 indicators according to municipal functional responsibilities. Third, candidate indicators were screened and refined using explicit SMART criteria to ensure operational relevance and data feasibility. Finally, the proposed framework was empirically examined through a validation exercise based on municipal sustainability reporting practices.

This sequential approach ensures conceptual coherence across stages while allowing the framework to remain grounded in real-world municipal governance and data constraints.

2.2. Structured Literature Review

The literature review aimed to inform the conceptual foundations of the framework rather than to provide an exhaustive or systematic mapping of the existing body of work. Its purpose was to identify key debates, methodological patterns, and recurring limitations in urban sustainability assessment, particularly in relation to indicator-based monitoring and SDG localization.

The review was conducted using the Scopus database, selected for its multidisciplinary coverage and relevance in sustainability, urban studies, and policy research [27]. Searches were carried out using combinations of the terms “sustainable cities”, “urban sustainability”, “indicators”, “metrics”, and “Sustainable Development Goals” or “SDGs”. To improve transparency in the literature review process, the search and selection procedure followed a structured screening logic inspired by PRISMA-style review approaches, while remaining consistent with scoping and narrative review practices commonly used in conceptual framework studies. The review focused on peer-reviewed journal articles and conference papers published from 2015 onwards and written in English, reflecting the period following the adoption of the 2030 Agenda [9].

Following this screening process, a refined set of studies was retained for detailed analysis. These publications provided the conceptual and methodological basis for identifying the main challenges associated with indicator-based urban sustainability assessment, including the operationalization of SDG targets, data availability constraints, and tensions between standardization and contextual relevance.

Rather than applying a formal systematic review protocol, articles were selected through iterative screening based on their relevance to three core themes: (i) urban sustainability assessment frameworks, (ii) indicator systems and performance measurement at the municipal level, and (iii) challenges associated with adapting global sustainability agendas to local governance contexts. Studies focusing exclusively on smart city technologies, highly sector-specific domains, or national-level assessments without urban or municipal relevance were excluded, consistent with established scoping and narrative review practices in the field [28,29].

The reviewed literature informed the identification of recurring gaps, including the limited operationalization of SDG targets at the city level, tensions between standardization and contextual relevance, and constraints related to data availability. These insights directly shaped the design choices adopted in the proposed framework.

2.3. Conceptual Framework Design and Target Reorganization

Framework development was guided by the principle that sustainability assessment systems should reflect the scope of action and decision-making authority of municipal governments. Instead of directly adopting existing classifications, sustainability dimensions were reorganized into six overarching categories aligned with typical municipal functions [22].

SDG targets were disaggregated and qualitatively analyzed at the target level, rather than at the level of entire goals. Each target was examined in terms of its substantive focus and relevance to municipal responsibilities. Targets were then assigned to one or more framework dimensions based on the area in which municipalities exert the most direct influence. In cases where targets spanned multiple domains, assignment followed a dominant-responsibility logic, prioritizing municipal actionability over thematic breadth. This approach aligns with recent calls for more granular and governance-aware SDG localization strategies [10,14].

To reduce potential subjectivity in the classification process, the allocation of SDG targets to the six framework dimensions was reviewed through an expert validation step. The expert panel included municipal sustainability practitioners, sustainability consultants, and standardization specialists with experience in urban sustainability assessment and indicator systems. These experts reviewed the proposed classification and confirmed the coherence between SDG targets, municipal governance responsibilities, and the conceptual structure of the framework. This validation step strengthened the transparency and reproducibility of the classification process.

In parallel, ISO 37120 indicators were reviewed and mapped onto the same six dimensions. Indicators that aligned clearly with municipal functions were retained, while those primarily dependent on national-level data or authority were identified as requiring adaptation or exclusion. This dual mapping process ensured conceptual consistency between global sustainability objectives and standardized urban performance indicators, while maintaining sensitivity to municipal governance realities [22,23].

2.4. Indicator Selection and Application of SMART Criteria

Indicator selection was guided by the SMART framework, which has been widely used in performance management and sustainability assessment to enhance clarity, feasibility, and accountability [24,30]. In this study, SMART criteria were operationalized as a qualitative screening tool rather than as a scoring or weighting mechanism.

Candidate indicators were assessed according to their specificity (clarity of definition and scope), measurability (availability of quantitative data and methodological transparency), achievability (feasibility within municipal authority and available resources), relevance (direct linkage to sustainability objectives and SDG targets), and time-boundedness (capacity for periodic monitoring). Particular emphasis was placed on data availability from public statistical sources, municipal databases, and international organizations, in order to enhance transparency and replicability [17].

To increase transparency in the application of SMART principles, the criteria used to assess each SMART dimension were further operationalized through a set of verifiable objective conditions. These conditions ensured that indicator selection followed consistent methodological rules rather than purely interpretative judgment. The application of SMART criteria resulted in a refined indicator set that prioritizes operational clarity, feasibility, and relevance for municipal decision-making. Rather than treating SMART criteria as a scoring or weighting mechanism, indicators were qualitatively screened to assess their suitability for monitoring at the city level.

Table 1. Operationalization of SMART criteria in indicator selection.

Indicator Characteristic	Verifiable Objective Criteria
Specific	Indicators were defined through the integration of SDG targets and ISO 37120 indicators and aligned with municipal governance responsibilities in Portugal and OECD contexts
Measurable	Data availability was verified through publicly accessible statistical databases, including international repositories and national databases such as the Portuguese Statistics Institute (INE) and Pordata. Indicators without publicly accessible municipal-level datasets were retained due to their inclusion in official SDG and ISO 37120 frameworks, which are expected by design to be measurable.
Achievable	Achievability was validated through consultation with municipal sustainability practitioners, sustainability consultants, and standardization experts, ensuring that indicators fall within realistic monitoring capacities
Relevant	Indicators were retained only if directly linked to SDG targets and to sustainability objectives within the scope of municipal responsibilities. Indicators outside municipal governance were excluded
Time-bound	Indicators were selected to ensure periodic data collection, typically on an annual basis, with some indicators available at quarterly or monthly intervals.

summarizes the operational criteria applied for each SMART characteristic.

The most common exclusion factors were related to insufficient data availability at the municipal level and to indicators primarily dependent on national authorities. Reformulation was more frequent among social and governance-related indicators, where conceptual relevance was high, but definitions required clarification to ensure measurability and periodic monitoring.

While many indicators were conceptually aligned with sustainability objectives, a non-negligible subset faced practical constraints related to data availability, institutional scope, or definitional clarity.

Table 2. Indicator Feasibility Outcomes Following SMART Screening.

Screening Outcome	Description	Typical Causes
Retained	Indicator fully meets SMART criteria	Clear definition, municipal data available
Reformulated	Indicator adapted for municipal applicability	Excessive aggregation, unclear scope
Excluded	Indicator removed from the final set	Data unavailable, outside municipal jurisdiction, ambiguous definition

summarizes the main outcomes of the SMART feasibility screening. Indicators that fell outside municipal jurisdiction, lacked reliable or regularly updated data, or were insufficiently defined for monitoring purposes were excluded or reformulated. This screening process aimed to balance conceptual ambition with operational feasibility, addressing a recurrent limitation identified in the urban sustainability assessment literature—namely, the proliferation of indicators that are theoretically relevant but practically unusable [8,18]. Data availability was confirmed in international databases such as United Nations statistical platforms and other global data repositories, as well as national databases such as the Portuguese Statistics Institute (INE) and Pordata. Indicators without publicly accessible municipal-level datasets were retained due to their inclusion in official SDG and ISO 37120 frameworks, which are expected by design to be measurable. Appendix A presents all indicators and their source—either public databases or SDG and ISO 37120 metrics.

2.5. Validation Through Municipal Case Analysis

To examine the practical applicability of the proposed framework, a validation exercise was conducted using sustainability-related reports published by the Porto City Council. The validation did not seek to evaluate municipal performance per se, but rather to assess the degree of alignment between existing municipal reporting practices and the structure and requirements of the proposed framework.

The validation followed a qualitative comparative approach. Indicators reported by the municipality were identified and categorized according to the six framework dimensions and subsequently compared with the proposed SMART indicator set. The analysis focused on three aspects: coverage of sustainability dimensions, alignment with municipal responsibilities, and availability of data suitable for monitoring over time.

This approach enabled the identification of areas of strong alignment, as well as systematic gaps, particularly in cross-cutting domains such as governance transparency, social equity, and long-term climate adaptation. Similar qualitative validation strategies have been widely used to assess the applicability and robustness of sustainability assessment frameworks in real-world governance contexts [20,25].

3. Results

3.1. Structure of the Integrated Urban Sustainability Framework

The primary result of this study is the development of an integrated framework for assessing urban sustainability through SMART indicators aligned with both the Sustainable Development Goals (SDGs) and ISO 37120. Rather than proposing a new set of indicators in isolation, the framework offers a structured architecture that reorganizes existing global and standardized indicators according to municipal functional responsibilities.

The framework consolidates urban sustainability assessment into six core dimensions: Government and Economic Development, Civic & Social Infrastructure, Environment and Climate, Infrastructure and Urban Planning, Health, and Urban Living Conditions. This reorganization directly addresses two recurrent limitations identified in the literature. First, the SDGs are frequently criticized for their abstract formulation and limited operational relevance at the municipal level. Second, standardized indicator systems such as ISO 37120, while methodologically robust, are often detached from explicit sustainability strategies and broader global policy agendas.

By integrating SDG targets and ISO 37120 indicators within a governance-oriented structure, the framework provides a coherent foundation for municipal sustainability planning, monitoring, and communication. Importantly, the six dimensions reflect areas in which municipalities typically exert direct or indirect influence, thereby strengthening alignment between sustainability assessment, institutional accountability, and local decision-making (

Table 3. Core Dimensions of the Urban Sustainability Framework.

Dimension	Scope and Rationale
Government and Economic Development	Governance quality, economic resilience, institutional capacity, transparency, and fiscal sustainability
Civic & Social Infrastructure	Access to and quality of education, culture, social services, and basic utilities
Environment and Climate	Resource efficiency, emissions, biodiversity, waste management, water resources, and climate adaptation
Infrastructure and Urban Planning	Mobility, energy systems, land use, digital infrastructure, and urban form
Health	Public health outcomes, prevention, environmental health, and access to healthcare
Urban Living Conditions	Housing, safety, social inclusion, equity, and overall quality of life

).

This categorization ensures alignment with municipal competencies, responding to critiques that sustainability assessment frameworks often fail to clearly distinguish between national and local responsibilities.

3.2. Alignment of SDG Targets and ISO 37120 Indicators

A key result of this study lies in the systematic decomposition of the Sustainable Development Goals into their constituent targets and the subsequent reassignment of these targets to the six framework dimensions, considering the institutional scope and responsibilities of municipalities. This target-level approach avoids the conceptual oversimplification associated with assigning entire SDGs to single domains and reflects the inherently cross-cutting nature of sustainable development challenges.

Table 4. Example of SDG-ISO 37120 Alignment.

Urban Dimension	SDG Targets	ISO 37120 Indicator Themes
Government and Economic Development	1.1, 1.2, 1.b, 2.b, 2.c, 5.5, 5.a, 8.1, 8.2, 8.4, 8.9, 8.10, 9.2, 9.3, 10.1, 10.4, 12.1, 12.6, 12.7, 12.8, 12.c, 13.2, 14.a, 15.9, 15.b, 16.5, 16.6, 16.7, 17.1, 17.6, 17.13, 17.14, 17.15, 17.16, 17.17	Economy, Finance, Governance
Civic & Social Infrastructure	3.7, 3.8, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.a, 5.1, 5.6, 5.c, 6.1, 6.2, 7.1, 8.3, 8.5, 8.6, 8.b, 10.2, 10.3, 13.3, 16.3, 16.9, 16.10, 16.b, 17.18, 17.19	Education, Recreation, Sports, and Culture
Environment and Climate	2.3, 2.4, 2.5, 6.3, 6.4, 6.5, 6.6, 6.b, 11.6, 12.3, 12.4, 12.5, 14.1, 14.2, 14.3, 14.4, 14.5, 14.6, 15.1, 15.2, 15.3, 15.4, 15.5, 15.7, 15.8, 15.c	Environment, Solid Waste, Water
Infrastructure and Urban Planning	7.2, 7.3, 9.1, 9.4, 9.5, 9.b, 11.1, 11.2, 11.3, 11.4, 11.5, 11.a, 11.b, 13.1	Energy, Transportation, Urban Planning
Health	2.1, 2.2, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.9, 3.a	Health, Food Safety
Urban Living Conditions	1.3, 1.4, 1.5, 5.2, 5.3, 5.4, 8.7, 8.8, 10.7, 10.c, 11.7, 16.1, 16.2, 16.4, 16.a	Housing, Social and Population Conditions, Security

presents the alignment between selected SDG targets and ISO 37120 indicator themes across the six framework dimensions.

In parallel, ISO 37120 indicators were mapped to the same dimensions, enabling a systematic comparison between global sustainability targets and standardized urban performance indicators within a common municipal governance structure.

Beyond illustrative alignment, the mapping process revealed uneven distributions of SDG targets and standardized indicators across the framework dimensions. To make these differences explicit,

Table 5. Mapping Density of SDG Targets and ISO 37120 Indicators.

Dimension	Relative Density of SDG Targets	Relative Density of ISO 37120 Indicators	Coverage Characterization
Government and Economic Development	High	Moderate	Governance-heavy, partial standardization
Civic & Social Infrastructure	Moderate	Moderate	Balanced but fragmented
Environment and Climate	High	High	Strong alignment and data availability
Infrastructure and Urban Planning	Moderate	High	Strong standardization, partial SDG linkage
Health	Moderate	Low	SDG-driven, limited standardized indicators
Urban Living Conditions	Moderate	Moderate	Social focus, mixed measurability

summarizes the relative density of SDG targets and ISO 37120 indicators for each dimension.

These patterns provide an empirical basis for the subsequent development and operationalization of the proposed framework, as presented in the following sections.

3.3. Conceptual Architecture of the Framework

Figure 1 presents the conceptual architecture of the integrated framework. The framework is structured as a three-layer system that links global sustainability objectives to municipal decision-support tools.

The first layer consists of SDG targets, representing global sustainability objectives. The second layer reorganizes these targets into six municipal sustainability dimensions and aligns them with ISO 37120 indicator themes. The third layer comprises SMART indicators supported by municipal and public data sources, enabling monitoring, benchmarking, and integration into digital dashboards and decision-support systems.

This layered structure clarifies how global agendas can be translated into operational municipal monitoring systems without sacrificing comparability or strategic coherence.

3.4. Framework Operationalization

Following the alignment of SDG targets and ISO 37120 indicator themes presented in Section 3.2, a critical step in the development of the proposed framework consisted of refining the applicability of the SDGs to the municipal scale. Although the SDGs provide a comprehensive and universally applicable reference, their scope encompasses objectives that extend beyond municipal responsibilities, including national-level governance, international cooperation mechanisms, and macroeconomic policy instruments. Accordingly, SDG targets whose implementation lies predominantly outside the domain of municipal action were either adapted to reflect local competencies or, where such adaptation was not feasible, excluded from the framework. This refinement ensured that the resulting model remains grounded in the institutional, operational, and policy capacities of urban governments, thereby enhancing its practical relevance for municipal sustainability assessment.

Once the set of SDG targets applicable to the municipal context was defined, a subsequent step consisted of consolidating these targets based on shared thematic affinities within each of the six framework dimensions. Rather than operationalizing individual SDG targets in isolation, this process led to the formulation of integrated objectives that capture coherent sustainability themes at the urban level. This consolidation was intended to reduce fragmentation across policy domains and to ensure that the proposed framework does not constrain the inclusion of interrelated aspects that are essential for an adequate assessment of the multiple and interconnected components of urban sustainability.

To operationalize the integrated objectives defined within each framework dimension, a structured set of indicators was established to support the assessment and comparison of urban sustainability across municipalities. In addition to the indicators proposed within the SDG framework, urban indicators from ISO 37120:2018 [19] were incorporated to enhance standardization and comparability, together with other indicators commonly employed by international organizations and municipal authorities. Indicator selection was guided by considerations of relevance, conceptual clarity, and feasibility at the municipal level.

Data availability constituted a key criterion throughout this process. Nevertheless, for a limited subset of indicators included in the framework, no publicly accessible online databases providing relevant data were identified at the time of analysis. As these indicators originate from official reference frameworks such as the SDGs and ISO standards, they were retained in the model. Such indicators are explicitly distinguished within the framework to ensure transparency regarding current data availability and to support future data collection and monitoring efforts.

Although not all indicators were found in the sustainability reports published by the Porto City Council, all indicators included in the framework correspond to datasets available in publicly accessible statistical repositories. These include international databases such as United Nations statistical platforms and other global data repositories, as well as national databases such as the Portuguese Statistics Institute (INE) and Pordata. Indicators without publicly accessible municipal-level datasets were retained due to their inclusion in official SDG and ISO 37120 frameworks, which are expected to be measurable. Consequently, the absence of some indicators in the municipal case study reflects limitations in current municipal reporting practices rather than inconsistencies in the framework itself. This distinction is important, as the proposed framework aims not only to monitor existing indicators but also to highlight areas where municipal sustainability monitoring systems can be expanded in the future.

To illustrate the operationalization of the proposed framework while preserving the readability of the main text, one framework dimension is presented in detail as an example. The Health dimension was selected for this purpose, as it encompasses targets and indicators drawn from multiple SDGs and highlights both strengths and limitations in terms of indicator standardization at the urban level (

Table 6. Health Dimension: SDG Targets and Operational Indicators.

SDG	Consolidated Target	Indicators
SDG 2	H1. End hunger and ensure access to nutritious, safe and sufficient food for all	Prevalence of undernourishment
		Prevalence of moderate or severe food insecurity
		Percentage of urban population undernourished
		Average distance to nearest supermarket
		Percentage of children experiencing food insecurity
		Proportion of population supported by food assistance programs
SDG 2	H2. Ensure balanced nutritional needs for all, particularly for vulnerable groups	Prevalence of malnutrition among children under 5 years of age
		Prevalence of anemia in women aged 15–49 years
		Percentage of urban population overweight or obese
		Prevalence of anemia by age group and sex
		Prevalence of micronutrient deficiency
		Percentage of newborns with low birth weight
SDG 3	H3. Reduce the maternal mortality ratio	Maternal mortality ratio
		Proportion of births attended by skilled health personnel
SDG 3	H4. End preventable deaths of newborns and children under five	Neonatal mortality rate
SDG 3	H5. Reduce the incidence of communicable diseases	Under-five mortality rate
		Number of infections per 1000 population, by disease
		Vaccination coverage rate, by vaccine type
SDG 3	H6. Reduce premature mortality from non-communicable diseases and promote mental health	Mortality from cardiovascular diseases, cancer, diabetes or chronic respiratory diseases
		Hospitalization rate for chronic diseases
		Suicide rate
		Antidepressant consumption
		Work absenteeism due to mental health problems
		Population reporting symptoms of depression or anxiety
SDG 3	H7. Reduce the harmful use of addictive substances	Prevalence of tobacco, alcohol and drug consumption
		Tobacco consumption per capita per day
		Users in rehabilitation programs per 1000 inhabitants
		Hospital admissions attributable to substance use
SDG 3	H8. Reduce mortality and illness from environmental and behavioral risks	Mortality attributed to household and ambient air pollution
		Annual mean concentration of PM2.5
		Noise pollution
		Air Quality Index
		Road traffic injury mortality rate
		Mortality attributed to unsafe water, sanitation and hygiene
		Mortality attributed to unintentional poisoning
		Deaths caused by natural disasters

).

For this dimension, the consolidated objectives, corresponding SDG targets, and associated indicators were defined to enable the assessment and comparison of population health conditions across municipalities. Within the Health dimension, eight targets were developed, drawing on SDGs 2 and 3. The complete table for the health dimension (with sources/origins for each indicator) is provided in the Appendix A.

The remaining framework dimensions are operationalized following the same structure and are fully presented in detail in Appendix A.

3.5. Validation Through the Porto Municipal Case

The proposed framework was validated through a comparative analysis of sustainability-related reports and publicly available indicators published by the Porto City Council. This validation aimed to assess the extent to which existing municipal monitoring practices align with the framework dimensions, consolidated objectives, and indicators, as well as to identify systematic gaps in current reporting.

The validation process involved mapping the indicators currently reported by the municipality to the six framework dimensions and their corresponding consolidated objectives. This mapping revealed a high degree of conceptual alignment, particularly in the Environment and Climate, Infrastructure and Urban Planning, and Civic & Social Infrastructure dimensions, where a substantial proportion of municipal indicators could be directly associated with the proposed framework. These areas correspond to domains in which municipalities typically hold clearer operational responsibilities and more established data collection practices.

To provide an overview of this alignment,

Table 7. Coverage of Framework Dimensions by Sustainability Indicators Reported by the Porto City Council.

Framework Dimension	Coverage by Existing Municipal Indicators	Main Gaps Identified
Government and Economic Development	Low to moderate	Governance transparency and institutional performance indicators
Civic & Social Infrastructure	Moderate to high	Equity-related service access indicators
Environment and Climate	High	Long-term climate adaptation indicators
Infrastructure and Urban Planning	High	Integrated land-use and resilience indicators
Health	Moderate	Mental health and preventive care indicators
Urban Living Conditions	Moderate	Social equity, vulnerability, and safety-related indicators

summarizes the coverage of the proposed framework dimensions by existing municipal indicators, distinguishing between dimensions with high, moderate, and limited levels of indicator availability.

Despite this overall alignment, the validation exercise also revealed systematic gaps across specific framework dimensions. Indicators related to governance transparency, social equity, and long-term climate adaptation were found to be weakly represented or entirely absent from existing municipal reporting. Importantly, these gaps do not reflect a lack of relevance at the urban level; rather, they highlight persistent challenges related to indicator definition, data availability at the municipal scale, and coordination across administrative departments.

These limitations are further illustrated in Figure 2, which compares the number of indicators included in the proposed framework with those for which data are currently available at the municipal level. The figure highlights the uneven distribution of data availability across dimensions, reinforcing the need for targeted improvements in municipal data systems and cross-departmental data integration.

Overall, the validation confirms the practical applicability of the proposed framework and demonstrates its diagnostic value. Beyond supporting urban sustainability assessment and inter-city comparability, the framework provides a structured basis for identifying blind spots in municipal sustainability monitoring and for guiding future indicator development and data collection efforts at the urban level.

4. Discussion

4.1. Advancing the Localization of the SDGs Through Municipal Logic

One of the central contributions of this study lies in its explicit focus on the localization of the Sustainable Development Goals through a municipal logic of action and responsibility. Although the importance of local governments in achieving the SDGs is widely acknowledged, the literature consistently highlights a persistent gap between global ambition and local operationalization [11,14,15]. This gap is commonly attributed to the abstract formulation of SDG targets, their cross-sectoral nature, and the limited jurisdictional authority of municipalities across several policy domains.

By disaggregating the SDGs into their constituent targets and associating them with functional areas corresponding to municipal responsibilities, the proposed framework directly addresses a core weakness of many existing localization approaches. Rather than treating the SDGs primarily as a reporting or communication exercise, the framework reframes them as an operational governance tool capable of informing municipal planning, monitoring, and prioritization. This target-level adaptation responds to repeated calls in the literature for more granular, context-sensitive, and action-oriented interpretations of the SDGs at the urban scale [13].

Importantly, this approach avoids the oversimplification observed in several SDG localization efforts, where entire goals are assigned to single policy domains, thereby masking trade-offs, synergies, and institutional interdependencies [10]. Instead, the framework reflects the systemic nature of urban sustainability, recognizing that governance quality, infrastructure provision, environmental management, and social conditions are deeply interconnected within municipal decision-making processes.

4.2. Integrating Standardization and Contextual Relevance

A persistent tension in sustainability assessment concerns the balance between standardization and contextual relevance. Highly standardized frameworks enhance comparability and benchmarking but often risk overlooking local institutional arrangements and policy priorities. Conversely, context-specific indicator sets may be more meaningful locally but limit cross-city learning and comparability [17,23].

The integration of ISO 37120 within the proposed framework represents a deliberate attempt to reconcile this tension. ISO 37120 has been widely recognized for its methodological rigor and international comparability, particularly in relation to Civic & Social Infrastructure and quality of life [20,21]. However, when applied in isolation, standardized indicator systems may become detached from strategic sustainability objectives and long-term policy agendas.

By embedding ISO 37120 indicators within a structure explicitly aligned with SDG targets and municipal responsibilities, the framework enhances the strategic interpretability of standardized metrics. This integration allows municipalities to situate performance indicators within a broader sustainability narrative, strengthening coherence between monitoring, planning, and reporting processes. Although similar integrative approaches have been advocated conceptually, empirical applications at the municipal level remain limited [21,22], reinforcing the relevance of the contribution presented here.

4.3. The Role and Limits of SMART Indicators in Urban Sustainability

The use of SMART indicators constitutes another key dimension of the proposed framework. SMART criteria have long been promoted in performance management and public policy to enhance clarity, accountability, and measurability [23,29]. In the context of urban sustainability, their application responds directly to criticisms regarding vague, aspirational, or non-operational indicators that fail to support decision-making [8,16].

The results indicate that applying SMART principles improves indicator feasibility and strengthens alignment with available data sources and municipal competencies. This finding is particularly relevant given the recurrent data limitations reported by cities attempting to monitor SDG progress at the local level [2,17]. By prioritizing measurability and time-boundedness, the framework supports longitudinal monitoring and performance tracking, both of which are essential for effective sustainability governance.

At the same time, the literature cautions against an overly technocratic reliance on quantitative indicators. SMART metrics may underrepresent qualitative dimensions such as social cohesion, institutional trust, democratic participation, and perceived well-being [6,30]. This limitation is explicitly acknowledged in the proposed framework, which is not intended to replace qualitative or participatory assessment approaches, but rather to complement them by providing a robust and transparent quantitative backbone for municipal sustainability monitoring.

4.4. Comparison with Existing Assessment Approaches

When positioned within the broader landscape of urban sustainability assessment tools, the proposed framework occupies an intermediate position between composite indices and indicator-based dashboards.

Composite indices offer simplicity and communication advantages but often rely on normalization procedures, weighting schemes, and aggregation rules that introduce methodological arbitrariness and obscure trade-offs between sustainability dimensions [24,31]. Such approaches may limit transparency and reduce their usefulness for policy learning and accountability.

In contrast, SDG dashboards and indicator lists emphasize transparency and disaggregation but frequently suffer from fragmentation and limited municipal granularity. Many SDG dashboards are designed for national or regional reporting and rely on indicators that are misaligned with municipal responsibilities or unavailable at the city scale [11,17].

The framework proposed in this study seeks to overcome these limitations by combining the transparency of indicator-based approaches with a coherent governance-oriented structure. By avoiding composite scoring while organizing indicators into intelligible municipal dimensions aligned with the SDGs and ISO 37120, the framework supports interpretability, accountability, and policy relevance simultaneously.

4.5. Governance Implications and Digital Decision-Support Systems

From a governance perspective, the proposed framework has significant implications for municipal decision-making and policy integration. By structuring indicators around municipal functions rather than sectoral silos, the framework facilitates horizontal coordination across departments—a challenge frequently identified in urban sustainability governance [5,12].

Moreover, the framework is inherently compatible with digital decision-support systems and emerging approaches to data-driven governance. The structured linkage between SDG targets, standardized indicators, and municipal data sources enables integration into digital dashboards, benchmarking platforms, and continuous monitoring systems. Such digital quality systems can support feedback loops between performance measurement, strategic planning, and policy adjustment, reinforcing adaptive governance capacities [2,32].

Beyond digital monitoring, the indicator framework can also be embedded within core municipal governance processes. In practical terms, sustainability indicators may support strategic planning cycles, departmental performance monitoring, and annual sustainability reporting conducted by municipal administrations. The structured indicator set also facilitates the identification of priority policy areas where environmental or social performance gaps are most significant, thereby supporting more informed allocation of municipal resources and budgetary planning. In addition, the framework can serve as a reference structure for municipal performance evaluation systems, enabling local governments to track progress toward sustainability objectives and align policy interventions with measurable outcomes.

In this sense, the framework extends beyond static reporting tools, offering a foundation for dynamic sustainability management aligned with smart governance and performance-based public administration paradigms.

4.6. Limitations and Threats to Validity

Several limitations and threats to validity should be acknowledged. First, the mapping of SDG targets and indicators to sustainability dimensions involves a degree of interpretative judgment, introducing potential subjectivity despite the use of explicit criteria. Second, the framework’s applicability is partly constrained by data availability, which varies significantly across municipalities and policy domains. Third, the empirical validation focused on a single municipal case within a developed-country context, limiting the generalizability of the findings to other governance settings.

These limitations do not undermine the conceptual contribution of the framework but instead highlight the need for further empirical testing across diverse institutional and geographic contexts.

5. Conclusions

This study proposed an integrated SMART indicator framework for urban sustainability assessment, explicitly designed to align the Sustainable Development Goals with ISO 37120 and the functional responsibilities of municipal governments. By disaggregating SDG targets, reorganizing standardized indicators according to municipal logic, and applying SMART criteria as an operational screening tool, the framework addresses key limitations identified in existing approaches to urban sustainability monitoring, particularly those related to actionability, comparability, and governance relevance.

The results demonstrate that global comparability and local relevance are not mutually exclusive. Rather, they can be reconciled through a structured, governance-oriented approach to indicator design and organization. The validation exercise confirmed the applicability of the framework in a real municipal context and highlighted its capacity to enhance transparency, identify performance gaps, and support evidence-based policy development. Beyond monitoring, the framework functions as a diagnostic and decision-support tool, enabling municipalities to better align sustainability objectives with operational responsibilities and available data.

From a practical perspective, the framework can be adopted by municipalities as a baseline structure for sustainability assessment, providing a common reference aligned with international agendas and standardized indicators. Municipalities are encouraged to use this baseline while developing documented local extensions tailored to specific territorial priorities or policy challenges. Such extensions should be explicitly recorded in order to preserve transparency and avoid compromising cross-city comparability.

The framework also lends itself to pilot multi-city applications involving a small group of municipalities (e.g., three to five cities) willing to jointly test indicator alignment, benchmarking practices, and reporting consistency. These pilot initiatives could support peer learning, identify data harmonization challenges, and contribute to the refinement of governance arrangements for sustainability monitoring.

Effective implementation further requires explicit data governance arrangements. Municipalities should define clear data ownership, data collection periodicity, quality assurance procedures, and mechanisms for data validation and auditing. Embedding the framework within an institutionalized data governance or digital quality system can enhance reliability, accountability, and continuity over time, reinforcing the role of sustainability assessment as an integral component of municipal management rather than a standalone reporting exercise.

Several avenues for future research emerge from this work. First, broader empirical validation across multiple cities and national contexts would strengthen the generalizability of the framework and enable systematic comparative analyses of urban sustainability performance. Applying the framework longitudinally would also allow for the examination of sustainability trajectories, policy effectiveness, and institutional learning over time.

Second, future studies should explore the integration of qualitative, participatory, and perception-based indicators, particularly in domains such as governance quality, social inclusion, and citizen engagement. Combining SMART quantitative indicators with deliberative assessment methods could provide a more comprehensive understanding of urban sustainability outcomes.

Third, the digitalization of the framework represents a promising research and practice-oriented direction. Integrating the indicator system into digital dashboards and decision-support platforms could facilitate real-time monitoring, scenario analysis, and adaptive policy experimentation, aligning with emerging paradigms of data-driven and performance-oriented urban governance.

Finally, future research should examine how governance-oriented sustainability frameworks can support cross-level policy alignment, facilitating coherence between municipal, regional, national, and international sustainability strategies. Such multilevel integration is essential to ensure that local sustainability efforts contribute meaningfully to the achievement of the 2030 Agenda.