5 Pointwise Mapping Models
The alternative to the MCT is a class of models concerned with the point-to-point photospheric
mapping 
. Each field line can be considered to be topologically unique, since every footpoint is
distinct from every other. Some authors prefer instead to think of every field line as topologically equivalent
by allowing footpoints to be continuously moved except across PILs. In either case, separatrices in
these models are defined by discontinuities in the footpoint mapping. This definition opens
the door for the quasi-separatrix layer (QSL, see Section 5.2), where the mapping is “almost”
discontinuous.
