A CmpMap is a compound Mapping which allows two component
Mappings (of any class) to be connected together to form a more
complex Mapping. This connection may either be "in series"
(where the first Mapping is used to transform the coordinates of
each point and the second mapping is then applied to the
result), or "in parallel" (where one Mapping transforms the
earlier coordinates for each point and the second Mapping
simultaneously transforms the later coordinates).
Since a CmpMap is itself a Mapping, it can be used as a
component in forming further CmpMaps. Mappings of arbitrary
complexity may be built from simple individual Mappings in this