Observations of ionospheric processes and signatures can provide an very powerful tool for a better understanding of magnetospheric dynamics because they provide two-dimensional images of magnetospheric processes. The magnetospheric origin of ionospheric signatures (and vice versa) can be determined by using a mapping along a model magnetic field for a particular level of magnetospheric activity. Such studies have provided much insight into the structure of magnetospheric boundaries. They require, however, much care for time dependent processes which are characteristic for periods of auroral and magnetospheric activity. A mapping along a model magnetic field requires that information is indeed transported along field lines, that the actual field is sufficiently well represented by the model field, and that the information is not modified by physical process in the inner magnetosphere. Another problem is the timing of processes respectively the speed with which information is exchanged. A beam of field aligned electrons which is generated at the magnetospheric boundary will reach the ionosphere significantly earlier than an Alfven wave which is generated at the same time and location. These aspects of the mapping of magnetospheric boundaries will be addressed in more detail.