  We study in experiment and with computer simulation the free energy and the
kinetics of vacancy and interstitial defects in two-dimensional dipolar
crystals. The defects appear in different local topologies which we
characterize by their point group symmetry; $C_n$ is the n-fold cyclic group
and $D_n$ is the dihedral group, including reflections. The frequency of
different local topologies is not determined by their almost degenerate
energies but dominated by entropy for symmetric configurations. The kinetics of
the defects is fully reproduced by a master equation in a multi-state Markov
model. In this model, the system is described by the state of the defect and
the time evolution is given by transitions occurring with particular rates.
These transition rate constants are extracted from experiments and simulations
using an optimisation procedure. The good agreement between experiment,
simulation and master equation thus provides evidence for the accuracy of the
model.
