## 1 What Is a Smart City  
In recent years, the term \"Smart Cities\" has become popular in Europe and abroad. There are various definitions of the term, but none of them are generally accepted. IBM was the first technologically leading company to discuss the Smart City Initiative in 2008. They introduced first concept of a Smart City:  
_\"Cities are gaining greater control over their development, economically and politically. Cities are also being empowered technologically, as the core systems on which they are based become instrumented and interconnected, enabling new levels of intelligence. In parallel, cities face a range of challenges and threats to their sustainability across all their core systems that they need to address holistically. To seize opportunities and build sustainable prosperity, cities need to become smarter\"_[1].  
According to IEEE [2],  
_\"A Smart City brings together technology, government and society to enable the following characteristics: a smart economy, smart mobility, a smart environment, smart people, smart living, and smart governance\"._  
The definition of European Commission, which promotes the general interests of the EU by proposing and enforcing regulatory compliance and implementing policies and the budget, is:  
_\"A smart city is a place where traditional networks and services are made more efficient with the use of digital solutions for the benefit of its inhabitants and business. A smart city goes beyond the use of digital technologies for better resource use and less emissions. It means smarter urban transport networks, upgraded water supply and waste disposal facilities and more efficient ways to light and heat buildings. It also means a more interactive and responsive city administration, safer public spaces and meeting the needs of an ageing population\"_[3].  
The last example of definition of Smart City is from Department for Business Innovation & Skills:  
_\"The concept is not static: there is no absolute definition of a smart city, no end point, but rather a process, or series of steps, by which cities become more,livable\" and resilient and, hence, able to respond quicker to new challenges. Thus, a Smart City should enable every citizen to engage with all the services on offer, public as well as private, in a way best suited to his or her needs. It brings together hard infrastructure, social capital including local skills and community institutions, and (digital) technologies to fuel sustainable economic development and provide an attractive environment for all\"_[4].  
When we look at the definitions, several key concepts can be extracted. Such selection of the major principles is summarized below:  
1. Technology is a necessary tool, but it cannot be the purpose and aim of Smart Cities;
2. The focus is on providing services for citizens and making cities more livable (e.g., concepts such as 15-min cities);
3. Smart Cities seek to optimize their processes by increasing integration (i.e., syneric effect);
4. Building a Smart City is a process and cannot be simply bought;
5. Changing the way of thinking among not only citizens (e.g., ownership versus shared economy) but also decision makers (e.g., citizens' involvement in projects);
6. Smart city projects shall meet one or more of the following objectives a. Improving quality of life; b. Using resources more efficient; c. Improving city sustainability; d. Improving city resiliency and citizens' safety with focus on critical infrastructure.
7. Others  
Smart Cities seek to optimize their systems by increasing integration through approaches such as increased interoperability, seamless system integration, and automation. Thus, they have the potential to deliver substantial efficiency gains and eliminate redundancy. To add to the complexity of the problem, it shall be stated that the integration of systems for efficiency gains may on the other hand compromise the resilience of an urban system. This all needs to be taken into consideration when thinking about Smart Cities.