102 ITU‐T's Technical Reports and Specifications Ref. No. Category Definitions/Features Key concept/ Keywords Source 91 User centric The definition of sustainable development comprises five categories: (i) Basic needs: Access to safe water, sufficient living space, adequate health care, and education are fundamental priorities for urban populations. (ii) Resource efficiency: A city's efficiency in such areas as the use of water and energy and the effective recycling of waste directly correlates to the quality of life of its citizens. (iii) Environmental cleanliness: Limiting exposure to harmful pollutants is fundamental to a city's liveability. (iv) Built environment: Equitable access to green space, public transportation, and dense, efficient buildings makes communities more liveable and efficient. (v) Commitment to future sustainability. An increase in the number of employees and the level of financial resources devoted to sustainability suggests how committed city governments are to implementing national and local policies and standards. Water, living space, health care, urban populations, energy, recycling, quality of life, pollutants, cleanliness, efficient, policies and standards. Bouton et al. (2012)