  The ground state properties of the Shastry-Sutherland model in the presence
of an external field are investigated by means of variational states built up
from unpaired spins (monomers) and singlet pairs of spins (dimers). The minimum
of the energy is characterized by specific monomer-dimer configurations, which
visualize the magnetic order in the sectors with fixed magnetization M=S/N. A
change in the magnetic order is observed if the frustrating coupling alpha
exceeds a critical value alpha_c(M), which depends on M. Special attention is
paid to the ground state configurations at M=1/4, 1/6, 1/8.
