  The paper focuses on the problem of localization in quantum mechanics. It is
well known that it is not possible to define a localization observable for the
photon by means of projection valued measures. Conversely, that is possible by
using positive operator valued measures. On the other hand, projection valued
measures imply a kind of localization which is stronger than the one implied by
positive operator valued measures. It has been claimed that the norm-1 property
would in some sense reduce the gap between the two kind of localizations. We
give a necessary condition for the norm-1 property and show that it is not
satisfied by several important localization observables.
