It goes like this: there are three levels of auto-image (barring the physical embodiment) where you can have one out of four options; man, boy, woman, or girl (there is also lass and lad, but for the purposes of this thread they will be treated as woman and man, since they are simply a variation (or sort of an adolescent Man or Woman)).
So there are three positions; the first position is your external autoimage, the second position your internal auto-image, and the third position your deep auto-image (might be unbeknownst to the holder).
So for example, a person can be a Man externally (or this person thinks they appear as a Man) , a Woman internally (they really think themselves a Woman) and deeply, they are in reality a Boy. So that would be Man-Woman-Boy (Combined Gender Identity).
[ External Identity - Internal Identity - True Identity ]
People can be typed using this system and VI can be used.