A definition of empirical anisotropy is proposed, which allows for a quantitative measurement. This theory is applied to RNA free energy landscapes. It is shown that the biophysical GCAU landscapes are highly anisotropic, while the synthetic GCXK landscapes become isotropic for long chains. The major part of the anisotropy of the GCAU landscapes arises from the difference of the G=C and the A=U stacking parameters.