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With nearly 70% of the world population expected to live in cities by 2050, assessing the sustainability of urban systems, both existing and future ones, is becoming increasingly relevant. Making cities more sustainable is a global priority, which is highlighted by 'Sustainable Cities and Communities' being listed as one of the Sustainable Development Goals (SDG) adopted by United Nations Member States in 2015. This Virtual Special Issue (VSI) explores the implementation and assessment of policies and technologies that contribute to the transition to a sustainable, energy efficient and regenerative society. We organized the issue according to four main research themes: 1) Renewable Energy Systems (i.e., different types of systems, qualitative assessments and public acceptance); 2) Sustainable Built Environment (which includes construction, operation and refurbishment); 3) Multi-Scale Models (considering urban sustainability transition from building to districts, or cities and regions to multi-country comparisons and their scaling across different countries); and 4) Governance and Policy (climate change mitigation and adaptation plans/policies that are reported across countries, urban services and infrastructures). This paper serves two purposes. The first is to provide an analysis about patterns, correlations and synergies found across the different topics that have been addressed over the last 20 years in the literature about cities' sustainability paths. A bibliometric analysis and a contingency matrix show the degree of correlation between scientific journals and main topics addressed by published articles. Secondly, the paper acts as an Editorial to the VSI, introducing the wealth of research articles and topics included in it. Both the bibliometric analysis and the papers published in this VSI demonstrate the interconnectedness of energy consumption, pollutant emissions and the competition for finite resources. The aim is to present advances and challenges of this exciting and ever-evolving research field to inform and guide future studies of urban sustainability. • We carried out a bibliometric analysis of the literature using the Cortext Manager platform· Using network analysis of a corpus of paper spanning 20 years we identified 8 major clusters. • The paper serves also as editorial for a virtual special issue dealing with urban sustainability pathways. • The virtual special issue is organised in four main themes, which touch upon different Sustainable Development Goals. [ABSTRACT FROM AUTHOR]

Abstract: Urbanization is a demographic, economic, and land transformation process. Building construction and operation are integral aspects of urban land use change and contribute to material and energy resources consumption and the resulting carbon dioxide (CO2) emissions in urban areas. In this paper, we ask two questions regarding the urbanization process: 1) Do the land, material, and energy use efficiencies associated with the construction and operation of buildings increase over time? 2) Do the gains in resource use efficiencies offset the increases in resource demands due to the magnitude of urbanization? To answer these questions, we use a systematic approach similar to a material flow analysis and apply it to the Pearl River Delta, a rapidly urbanizing region in China. We use a combination of satellite data and official statistics to evaluate changes in urban population density and building density from 1988 to 2008. Both density measures decrease from 1988 to 2003; after 2003, building density increases while population density continues to decline. We also track the indirect impacts of urban land expansion on material and energy demands and associated CO2 emissions using concrete and heating/cooling as proxies for building construction and operation, respectively. Throughout the study period, structural changes and efficiency gains decrease the demand per unit floor area for both building materials and energy. However, the efficiency gains are outstripped by the magnitude of urban expansion, therefore leading to an increase in the demand for resources and CO2 emissions per capita. Our results show that focusing only on gains in efficiency for individual buildings without considering the scale of urban expansion results in underestimate of the cumulative energy, material, and greenhouse gas emissions impacts of urbanization. We emphasize the distinction between the rates versus the accumulations of these impacts over spatial and temporal scales. We discuss the relevance of the Environmental Kuznets approaches to tackling environmental impacts that are cumulative in nature and may lead to irreversible changes in the environment. We conclude that tracking the energy, materials, and emissions impacts of urbanization requires a multi-scale approach that ranges from the individual building to the urban region. [Copyright &y& Elsevier]

This section presents abstracts of papers on city planning published from 2007 to 2008, including "Streets, Sounds and Identity in Inter-war Harlem," by Clare Corbould, "(Re)making the Other, Heterosexualising Everyday Space," by Kath Browne, and "Rankings and Reactivity: How Public Measures Recreate Social Worlds," by Wendy Nelson Espeland and Michael Sauder.