The trajectory and the corresponding plastic deformation of a material element during equal channel angular extrusion (ECAE) are analyzed with the help of a flow line function applicable for any ECAE die angle. The function contains the following three parameters: the parameter n that describes the sharpness of the line and the a and m parameters that account for the asymmetry of the flow line. The approach permits to determine the velocity field, the strain rate field, and, in general, the shape of the plastic deformation zone in ECAE experiments even for flow lines that are asymmetric with respect to the ECAE geometry. The flow line function was applied to flow lines observed in 90 degrees and 120 degrees ECAE of commercially pure aluminum as well as for 135 degrees ECAE of pure copper to describe the characteristics of the deformation field and the evolution of the crystallographic texture.