56 ITU‐T's Technical Reports and Specifications Environment – The city must be sustainable in its functioning for the present as well as future generations. Governance – The city must be robust in its ability for administrating policies and pulling together the different elements. 3.3 Infrastructure – physical, service and digital Infrastructure in an urban environment can be best described in a threefold manner: physical, service and ICT or digital. Physical infrastructure is what is truly \"physical\" – for example, buildings, train tracks, roads, electric lines, gas pipelines, water, factories and the like. Service infrastructure is the service overlay on the physical aspects – for example, a transportation service such as Mass Rapid Transit ((MRT), bus), utilities (water, gas, and electricity), education and health care. The ICT infrastructure is essential for a successful smart sustainable city – it acts as the \"glue\" which integrates all the other elements of the smart sustainable city acting as a foundational platform. ICT infrastructure is at the core and acts as the nerve centre, orchestrating all the different interactions between the various core elements and the physical infrastructure. 4 Definitions and analysis 4.1 Sources of information This section presents a study of definitions and associated attributes in terms of indicators, indices and rankings of smart sustainable cities. For the purpose of this Technical Report, various articles were collected from the Internet as well as from other databases. These articles were reviewed and analysed to help consolidate a wide range of perspectives which ensures that the definition of smart sustainable cities proposed by the Focus Group includes all major aspects. These definitions were obtained from a variety of sources including: Academia and research communities. Government initiatives including EU. International organizations (United Nations, ITU, etc.). Corporate/company profiles. User centric definitions (from leading market research firms). Trade associations. Standards development organizations. A complete list of over all the definitions found in the open literature is stated in Annex 1. 4.2 Methodology Given the large amount of data, the various indicators, metrics and the 100+ definitions for a smart city, there was a need to perform some in‐depth analysis to determine what would be a comprehensive and inclusive definition of a smart sustainable city from the perspective of the work being undertaken by the Focus Group on Smart Sustainable Cities (FG‐SSC). All the definitions in Annex 1 were analysed to identify what makes a smart sustainable city. The results from this analysis which identified the top keywords and characteristics of a smart sustainable city are discussed in more detail in section 5.