These terms for some years recur in sector publications, even if the meaning is not always clear. Below I try to define them.

Viral sensing: acquisition of new data and information through existing digital networks, collecting the traces left by people in their daily activities (money transactions, displacements, fruitions of services ...), aggregating them in order to reconstruct the information landscapes which host social phenomena.

Sensor Network: networks of sensors to detect data related the town activities. A large mass of data, enriched with spatial and temporal reference, allows not only a description of the phenomena but also to create a virtual model of the environment for the domain of interest.

Crowd sensing: also known as the Internet of people, is based on the potentialities of social media tools typical of the web 2.0; individuals collect their experiences and share them in real time, influencing others in their choices; information that is collected is subjective, but the strong interaction between users reveals a precise description of the phenomena considered.For this reason it is an excellent way to obtain information about the social dynamics, acquiring contributions from any person without particular limitations. Instead, it is less suitable to collect scientific data, as in this case it is necessary to form a closed group of volunteers with appropriate training and equipment, defining the timing and method of data collection.
In urban areas, the data collected can be presented to the citizens through information devices installed at key locations in the city, also allowing the collection of user opinions.