802 ITU‐T's Technical Reports and Specifications 4 Abbreviations and acronyms These Technical Specifications use the following abbreviations and acronyms: AIDS Acquired Immune Deficiency Syndrome GDP Gross Domestic Product GHG Greenhouse Gas HIV Human Immunodeficiency Virus infection HLY Healthy Life Years ICT Information and Communication Technology ISO International Organization for Standardization ITU International Telecommunication Union KPI Key Performance Indicator PM10 Particulate Matter up to 10 micrometres in size PM2.5 Particulate Matter up to 2.5 micrometres in size QoL Quality of Life SSC Smart Sustainable City ToR Terms of Reference UN‐Habitat United Nations Human Settlements Programme 5 General principles for key performance indicators for ICT in a city context The selection of KPIs is based on the following principles: Comprehensiveness: The set of indicators should cover all the aspects of SSC. The indicators for evaluation should be aligned to the measured subject, i.e., ICT and its impact on the sustainability of cities. The index system should reflect the level of general development for a certain aspect. Comparability: The KPIs should be defined in a way that the data can be compared scientifically between different cities according to different phases of urban development, which means the KPIs must be comparable over time and space. It should also be possible to extend and amend the set of KPIs according to the actual stage of development. Availability: The KPIs should be quantitative and the historic and current data should be either available or easy to collect. Independency: The KPIs in the same dimension should be independent or almost‐orthogonal i.e., overlap of the KPIs should be avoided as much as possible. Simplicity: The concept of each indicator should be simple and easy to understand. Also the calculation of the associated data should be intuitive and simple.