In 1999, before the advent of Foursquare, mobile Twitter clients or sensor-enabled phones, a somewhat prescient Neil Gross in Bloomberg Business Week said: "In the next century, planet earth will don an electronic skin. It will use the Internet as a scaffold to support and transmit its sensations." A new area of research called "citizen sensing" has emerged since then that aims to derive collective knowledge from the actions and reactions of individuals armed with internet-enabled mobile devices.
There are various advantages for human-in-the-loop sensing. For collecting data in large urban areas - for example, for environmental or traffic monitoring purposes - it can be both expensive and time consuming to build large networks of sensors in these areas. Having people walking around with sensor-enabled devices makes sense due to the high population densities in urban areas and the willingness of people to contribute sensor data if it will have an eventual positive impact on their lives.
More recently, a professor in Ohio's Wright State University, Amit Sheth, outlined the notion of 'citizen sensing' whereby people are, "Acting as sensors and sharing their observations and views using mobile devices and Web 2.0 services." A citizen sensor network is "an interconnected network of people who actively observe, report, collect, analyze, and disseminate information via text, audio or video messages." In particular, Sheth presented work in which semantic annotations were applied to Twitter microblog posts from 'citizen sensors' in order to provide situational awareness, e.g. in the Mumbai terrorist attacks.