The concept of smart city has become a key factor in urban sustainable development. It is a compilation of urban planning strategies and has many far-reaching benefits, including efficient allocation of resources, speed of policy implementation, seamless communication and a series of environmental benefits.

Nowadays, smart cities are booming in all corners of the world. Singapore, Copenhagen, Amsterdam and Oslo are indisputable leaders in this new trend. The following are four major smart city technologies that have been widely used in the development of modern smart cities.

1. Intelligent Internet of things devices

The new application of the Internet of things (IOT) enables smart cities to be practiced worldwide. This modern technology enables cities to remotely monitor, control and manage urban facilities and equipment, and create new insights and operable information from quantitative real-time data streams. The Internet of things has potential significance in the overall development of smart cities, especially in enhancing urban connectivity. These IOT devices include smart sensors, actuators, monitoring devices and AI projects. Through these devices, cities can significantly improve the accessibility and mobility of cities, promote social inclusiveness, improve energy efficiency, and finally achieve the goal of sustainable development.

A typical example of smart city IOT is the smart sensor on Oslo road light. Oslo intelligent street lighting project is a city wide project aimed at improving the efficiency of street lighting systems. Oslo integrates the city's street lighting into a single remotely accessible network that can use Internet-based applications for lighting level management and monitoring. The E-street system can adjust the light intensity according to the time of year and the needs of specific circumstances, and further optimize the energy use of the city. The 20000 smart street lamps in Oslo contribute nearly 70% to energy conservation.

With the widespread use of smart phones and mobile devices, citizens are encouraged to participate in urban ecology. With the gradual progress and expansion of Internet of things technology, citizens and governments are bound to connect in an unprecedented way.

However, challenges and disputes are accompanied by huge interests and opportunities, which makes the debate between public space and personal privacy become the focus. In smart cities, aggressive public data collection may pose a threat to citizens' privacy, increase the risk of cyber attacks, and also bring high costs and data discrimination. It is estimated that in the next 20 years, the city will invest a total of about $41trillion in infrastructure upgrading. Future urban planners and decision makers will have no choice but to assure the public that these dark aspects of Internet of things technology will not affect the morality and normal operation of the city.

2. Smart energy

Urban sustainability is an important part of smart cities. In order to achieve this goal, we must invest in efficient and environmentally friendly energy management.

In recent decades, with the rapid growth of urban agglomerations, the demand for energy supply has also soared. Sometimes it is higher than the availability of local resources. The long-term solution to the growing energy demand is the so-called smart energy chain, which relies entirely on renewable energy such as solar and wind energy. The system allows decentralized clean and sustainable energy to be transmitted to every corner of urban areas through intelligent digital systems.

The energylabnodhavn project in Copenhagen is one of the most representative and far sighted examples of smart energy. In order to achieve carbon neutrality by 2050, the city has begun to build a huge smart energy network. The initiative aims to address the issue of improving the flexibility of energy networks, which are increasingly dependent on intermittent energy. It reduces the peak load of the power grid by testing large batteries and electric vehicles, and deploys intelligent heating in 85 residential units to reduce the burden of heating circuits and improve indoor comfort. So far, more than 7000 families in the urban area have benefited from this initiative.

Although the concept of smart energy sounds promising, there are still some inevitable operational challenges to put it into practice. The accuracy of smart meters for measuring energy is difficult to be guaranteed at any time. In most cases, this misjudgment may lead to long-term energy waste and violate the goal of sustainable development. In addition, the integration of intelligent energy systems into larger urban operation mechanisms always requires technology and funds, which makes most developing cities may not be able to achieve in the near future.

3. Intelligent travel and transportation

Liquidity is the heartbeat of a city. Smart city transportation and transportation network have become the focus of many smart city initiatives. Urban areas such as multimodal transport, intelligent parking and intelligent traffic lights are usually included in this concept. This approach is based on rethinking the transportation infrastructure used in daily life, including not only traditional cars, electric vehicles and public transport, but also new and innovative forms of transportation, such as on-demand carpooling services (Uber and LYFT) and car sharing programs. The accessibility and livability of cities can be further established through these considerations.

Singapore is in an indisputable leading position in the experiment of intelligent travel. The city's intelligent transportation 2030 is a 15 year master plan, which plans how to develop the intelligent transportation system (ITS) in the country. This is a complex transportation network, including highway monitoring and consulting system, green road determination system, intersection electronic eye, traffic scanning, parking guidance system, electronic road toll collection and intelligent bus station. The mission of the plan is to use the latest its projects and transportation technology breakthroughs to optimize the transportation network in a sustainable way and improve the commuting travel experience in Singapore.

However, for most developing cities, many people believe that the case of Singapore does not have much reference. First, many communities lack the ability to mobilize the large amount of funds needed to support infrastructure projects. Secondly, urban transport infrastructure projects are difficult to plan and implement, especially in densely populated areas, land acquisition and resettlement issues may be extremely complex.

4. Intelligent building

The vigorous development of intelligent buildings is crucial to the long-term development of smart cities. Intelligent building refers to a building that uses digital based automatic programs to generate building systems, including lighting, processing equipment, pipelines, access control systems, digital signage, wayfinding systems, and security systems. In short, it is a building full of vitality and breathing organisms. A remarkable feature of this modern architecture is its ability to adapt to the climate, and it has foresight against the background of deteriorating climate problems. Technologically advanced buildings can easily reduce resource use and improve energy efficiency, simplify maintenance, reduce operating costs, and provide a cleaner environment for residents.

A groundbreaking example of intelligent architecture is theedge in Amsterdam. According to Bloomberg, edge is the most intelligent and environmentally friendly building in the world, with the highest sustainability score of 98.4%. More than 28000 sensors are installed inside the building, connecting everyone through mobile apps. The most avantgarde function is that the intelligent building can remember the schedule of each employee and provide them with instructions on where to go, so as to ensure that they appear in the right place at the right time.

Although revolutionary, the future of intelligent building still faces many difficulties. Architecture experts raised five major issues: acquisition costs and investment barriers, distrust of network security, proper planning and adequate maintenance, insufficient integration and cultural responsiveness. Although intelligent buildings are people-oriented, the boundary between digital connection and personal privacy seems to be blurred.