This note deals with recently developed gramian based interaction measures. The measures are used for the choice of measurement/actuator pairs for decentralized control, where the controller remains unspecified. The theoretical background of these measures is clarified and a geometrical interpretation is given. Moreover, a generalization of the Hankel interaction index array to different gramian based system norms is proposed and it is shown that the introduction of weighted gramians makes the criteria more flexible and superior compared to the augmenting with additional filter dynamics. Finally, some examples are given to illustrate the usefulness of the generalized measures.