Introduction to this special issue: semantic and symbolic trajectories

Nowadays, the digital traces of moving objects, such as people, animals, goods, increasingly contain richer information than the mere location history. Traces can report, for example, the places visited by tourists during a touristic journey (e.g., hotels, entertainment spots), the activities performed during such a journey (e.g., shopping, driving), the people encountered during the trip. This supplementary information is often referred to as semantic annotation (of trajectories). Semantic annotations can be directly acquired from sensors or, alternatively, be the result of some analytic process or be directly provided by users. In recent times, following a few pioneering research projects, especially in Europe and Asia, the processing of large amounts of semantics-enriched trajectories has become an exciting, cross-disciplinary research area, spanning spatial computing, data analytics and geographical information science. Semantics-enriched trajectories have important applications in a variety of domains, such as urban computing, social media analysis and animal ecology, especially in connection with the analysis of moving objects' behavior, both at individual and collective level.