So in GR the transformation between the curvilinear and the euclidian manifold results in a monometric which defines gravitational interactions.

In heim’s theory there is an intermediate transformation into heim space that gives rise to the heim polymetric.

The result of the polymetric is a hermetry from in which 12 subspaces corresponding to interactions are derived. 

By using heim space as an intermediate step, he was able unite GR and QT.