Cities today are dense networks of interchanging investments, information, goods and people, as well as centers of innovation and knowledge management. In such a complex framework of housing, social and economic interrelationships, cities become large consumers of resources and producers of greenhouse gases. Therefore, and in order to preserve resources and guarantee social services and the well-being of citizens, planning and policy actions are required that contribute to achieving sustainable growth. Beyond the environmental perspective, a socio-economic analysis is essential to make a comprehensive sustainability diagnosis of urban and rural systems. This paper presents a methodology for sustainability assessment, based on 38 indicators that include the three pillars of sustainability: social, economic and environmental. To carry out this assessment, 64 municipalities out of 313 located in Galicia (Northwest Spain) were selected and classified in three categories according to their population size (Medium Size, Small Size and Village). Moreover, two weighting methods have been considered (equal weighting and measured weighting attributed through Analytic Hierarchy Process method). The results show that most sustainable municipalities are located in the north of the region. On the other hand, regardless of the weighting method, 57% of the medium-sized municipalities are rated sustainable compared to 45% of those of the categories of Village and Small Size categories. Therefore, municipal size is relevant for measuring sustainability and there are no significant differences between the results obtained with the two weighting methodologies, indicating that the method developed is robust and could be applied to other municipalities and cities.

Introduction

The population of developed countries has experienced exponential growth since 1950 (Steffen et al., 2015), and the analysis of the statistics shows that about 50% of the population lives in urban areas (Ibrahim et al., 2018). The urban population is expected to multiply by 1.5 by 2045, which would mean a significant increase in the number of residents in urban areas, an additional 2 billion. Having this in mind, cities or urban settlements play a key role as driving forces of the global economy. Cities account for 85% of global gross domestic product (GDP) generation (World Bank, 2017), 75% of natural resources demand and 50% of global waste production (Ellen MacArthur Foundation, 2017). Therefore, urban systems are essential elements in global performance and are responsible for more than 70% of global greenhouse gas emissions (World Bank, 2018). Within this framework of growing expansion of the urban environment (Lopez-Carreiro and Monzon, 2018
), the quality and demand for resources (energy, water, nutrients), as well as socio-economic conditions in terms of living conditions, employment rates, cost of living are under increasing pressure (Ibrahim et al., 2018; Feleki et al., 2019). Bearing in mind the three pillars of sustainability: environmental, social and economic, the urban environment should not pose a threat to sustainable growth, but it could contribute positively if this development is properly managed by increasing productivity, materialising investment options, prioritising modernisation and posing new challenges to citizens, but always under intense policy coordination in the framework of sustainable development.