  In this paper, we study the clustering properties of the Spatial Preferential
Attachment (SPA) model introduced by Aiello et al. in 2009. This model
naturally combines geometry and preferential attachment using the notion of
spheres of influence. It was previously shown in several research papers that
graphs generated by the SPA model are similar to real-world networks in many
aspects. For example, the vertex degree distribution was shown to follow a
power law. In the current paper, we study the behaviour of C(d), which is the
average local clustering coefficient for the vertices of degree d. This
characteristic was not previously analyzed in the SPA model. However, it was
empirically shown that in real-world networks C(d) usually decreases as d^{-a}
for some a>0 and it was often observed that a=1. We prove that in the SPA model
C(d) decreases as 1/d. Furthermore, we are also able to prove that not only the
average but the individual local clustering coefficient of a vertex v of degree
d behaves as 1/d if d is large enough. The obtained results are illustrated by
numerous experiments with simulated graphs.
