This article is related to user privacy. Users' trajectory is an important information as an input in location recommendation systems. However, because it is a sensitive data, it should be protected w.r.t user privacy.
J. Bao, Y. Zheng, und M. Mokbel. Proceedings of the 20th International Conference on Advances in Geographic Information Systems, Seite 199--208. New York, NY, USA, ACM, (2012)