  An internal or friendly partition of a vertex set $V(G)$ of a graph $G$ is a
partition to two nonempty sets $A\cup B$ such that every vertex has at least as
many neighbours in its own class as in the other one. Motivated by Diwan's
existence proof on internal partitions of graphs with high girth, we give
constructive proofs for the existence of internal partitions in the incidence
graph of projective planes and discuss its geometric properties. In addition,
we determine exactly the maximum possible difference between the sizes of the
neighbor set in its own class and the neighbor set of the other class, that can
be attained for all vertices at the same time for the incidence graphs of
desarguesian planes of square order.
