  Enhanced sampling techniques such as umbrella sampling and metadynamics are
now routinely used to provide information on how the thermodynamic potential,
or free energy, depends on a small number of collective variables. The free
energy surfaces that one extracts by using these techniques provide a
simplified or coarse-grained representation of the configurational ensemble. In
this work we discuss how auxiliary variables can be mapped in collective
variable (CV) space and how the dependence of the average value of a function
of the atomic coordinates on the value of a small number of CVs can thus be
visualised. We show that these maps allow one to analyse both the physics of
the molecular system under investigation and the quality of the reduced
representation of the system that is encoded in a set of CVs. We apply this
approach to analyse the degeneracy of CVs and to compute entropy and enthalpy
surfaces in CV space both for conformational transitions in alanine dipeptide
and for phase transitions in carbon dioxide molecular crystals under pressure.
