# IoT-Enabled Smart Sustainable Cities: Challenges and Approaches
## 2 Overview on a Smart Sustainable City
### Sustainability Indicators  
As per definition [16], indicators can be described as \"_quantitative, qualitative or descriptive measures that enable information on a complex phenomenon, such as the dynamic urban environment, to be simplified into a form that is relatively easy to use and understand._\" Among their main functions (quantification, simplification, and communication), they show trends and changes in the measured phenomena, when periodically evaluated and monitored. Consequently, city indicators assist cities in setting targets and monitoring their performance over time and, at the same time, are also important in the municipality decision-making process. Recently, indicators are also employed by city management with the aim to increase transparency towards citizens through city dashboards showing real-time collected data which can be useful to citizens. Moreover, urban sustainability includes smartness indicators corresponding to tools that allow city planners, city managers, and policy-makers to estimate the socioeconomic and environmental impact of current urban designs, infrastructures, policies, waste disposal systems, pollution, and accessibility services by citizens. More in detail, they allow to detect problems and critical situations, identifying areas that would benefit from governance attention and technology-assisted responses. Finally, they allow cities to monitor the success and impact of sustainability interventions, while being extremely heterogeneous, and usually include aspects of sustainable development beyond environmental dimensions, such as public health and services, governance, income, business opportunities, and mobility. On the basis of proper indicators, each a municipality should decide which would be the ones best addressing the needs and goals of their city, which would be easy to implement, and which would be worth the financial and human efforts. In some cases, a selection of different tools may be desirable for a city with a small population; in others, a large city may want to join an established global program of indicators. In [17], the European Community (EC) provides a short guide for local government actors to the currently available indicator tools for sustainable smart cities, focusing on the environmental dimension. Looking at this analysis, the starting point is that, in order to create a sustainable urban environment, it is crucial to measure and assess policies; infrastructure; socioeconomic factors; resource use; emissions; and any other process that contribute to and profit from the city's metabolism, prosperity, and quality of life [18]. This will allow governments to identify areas of opportunity as well as concerns, and to respond by developing realistic sustainability goals with a long-term perspective. In order to choose the right sustainability indicator, it is important to understand the various purposes which indicators can be used for. Fundamentally, they can be applied in three ways:  
* _explanatory indicators_, corresponding to a well-defined set of indicators collected in order to evaluate the current state of the environmental dimension of sustainability in a city or urban area;
* _pilot indicators_, referring to indicators chosen specifically to assist policy-making; and
* _performance assessment indicators_, which are the most common ones and generally involve Key Performance Indicators (KPIs). Data availability is another aspect to be carefully considered when selecting indicators, as without good data--collected through proper monitoring--it is not possible to develop indicators. Moreover, as indicator sets must reflect the geographical and social context of the urban area they have to describe, they should be locally relevant and suitable for the scale (in terms of size, physical layout, and organizational structure) of the specific city or municipality.