  The light pollution levels experienced at any given site generally depend on
a wide number of artificial light sources distributed throughout the
surrounding territory. Since photons can travel long distances before being
scattered by the atmosphere, any effective proposal for reducing local light
pollution levels needs an accurate assessment of the relative weight of all
intervening light sources, including those located tens or even hundreds of km
away. In this paper we describe several ways of quantifying and visualizing
these relative weights. Particular emphasis is made on the aggregate
contribution of the municipalities, which are -- in many regions of the world
-- the administrative bodies primarily responsible for the planning and
maintenance of public outdoor lighting systems.
