  Galaxies and clusters distributions show two major properties: (i) the
positions of galaxies and clusters are characterized by a power law
distribution indicating properties with respect to their positions. (ii) The
distribution of masses is also characterized by a power law corresponding to
self similarity of different nature. These two properties are naturally unified
by the concept of multifractality. This concept naturally arises if the
distribution of matter, as given by both positions and masses, has self similar
properties. We discuss the experimental situation in this respect and we
introduce a simple stochastic model based of the aggregation process of
particles The aim of this model is to understand which characteristic
properties of the aggregation probability can gives rise to multifractal
distribution In particular we find that a crucial element in this respect is
that the aggregation probability should depend on the environment of the
aggregation region.
