Negative First Dimension
On negative first dimension, there is no point on this space.
In abstract polytopes, the -1D shape is the null polytope; this is a consequence of abstract polytopes also being sets since the null polytope corresponds to the empty set.
Negative Second Dimension
In the negative second dimension, there exists the -2D shape of the Dinull polytope. It has little physical meaning, even in the realm of abstract polytopes, but does show up in some places, such as in Cinioveres.