d Abstract] K. Buchin Dept. Computer Science Utrecht University The Netherlands buchin@cs.uu.nl M. Buchin Dept. Computer Science Utrecht University The Netherlands maike@cs.uu.nl J. Gudmundsson NICTA , Sydney Australia joachim.gudmundsson@ nicta.com.au We study the problem of detecting a single file behavior in a set of trajectories. A group of entities is moving in single file if they are following each other, one behind the other. This movement pattern occurs often, among animals, humans, and vehicles. It is challenging to detect because it does not have a fixed layout. In this paper we first model the notion of following behind, on which we base our definition of single file. We present efficient algorithms for detecting following behind and single file behaviors. We test and evaluate these algorithms on real and generated test data. Categories and Subject Descriptors H.4 [Information Systems Applications]: Miscellaneous-Geographic Information Systems; F.2.m [Analysis of Algorithm...