  The interaction between a graphene layer and a hexagonal Boron Nitride (hBN)
substrate induces lateral displacements and strains in the graphene layer. The
displacements lead to the appearance of commensurate regions and the existence
of an average gap in the electronic spectrum of graphene. We present a simple,
but realistic model, by which the displacements, strains and spectral gap can
be derived analytically from the adhesion forces between hBN and graphene. When
the lattice axes of graphene and the substrate are aligned, strains reach a
value of order 2\%, leading to effective magnetic fields above 100T. The
combination of strains and induced scalar potential gives a sizeable
contribution to the electronic gap. Commensuration effects are negligible, due
to the large stiffness of graphene.
