Heatherfield is the home town of the
W.I.T.C.H. girls. It's a fairly big city (Approx. 500 000 inhabitants), but very unusual in the
sense that it contains several
portals to
parallel dimensions. I.e. the house of
Eylon, which contain a portal to the dimension of
Meridian.
Heatherfield is a very international citym with large cooperations like Simultech and others. Not to mention all the people of different ethnic backgrounds. Hay Lin is of chineese descent, Taranee has African background and so on.
It is not clear where Heatherfield is located, but a good guess would be somewhere in California.