  A quantum walk whose continuous limit coincides with Dirac equation is
usually called a Dirac Quantum Walk (DQW). A new systematic method to build
DQWs coupled to electromagnetic (EM) fields is introduced and put to test on
several examples of increasing difficulty. It is first used to derive the EM
coupling of a well-known $3D$ walk on the cubic lattice. Recently introduced
DQWs on the triangular and honeycomb lattice are then re-derived, showing for
the first time that these are the only DQWs that can be defined with spinors
living on the vertices of these lattices. As a third example of the method's
effectiveness, a new $3D$ walk on a parallelepiped lattice is derived. As a
fourth, negative example, it is shown that certain lattices like the
rhombohedral lattice cannot be used to build DQWs. The effect of changing
representation in the Dirac equation is also discussed.
