  As a novel approach with possible relevance to semiclassical gravity, we
propose to define regions of space as quantum subsystems. After recalling how
to divide a generic quantum system into ``parts'', we apply this idea to a free
scalar field in Minkowski space and we compare two different localization
schemes. The first scheme is the standard one, induced by the local
relativistic fields; the alternative scheme that we consider is the one induced
by the Newton-Wigner operators. If degrees of freedom are divided according to
the latter, the Hamiltonian of the field exhibits a certain amount of
non-locality. Moreover, when a region of space is cut off from the rest
according to the Newton-Wigner scheme, the geometric entropy is finite and
exhibits a sensible thermodynamic behaviour.
