I think that the problem might be that the boundary between the two regions is not well-defined currently.
Wikipedia wrote:The country's name comes from the two regions Bosnia and Herzegovina, which have a very vaguely defined border between them. Bosnia occupies roughly the northern two thirds of the country, while the southern third is Herzegovina.
The major cities are the capital Sarajevo, Banja Luka in the northwest region known as Bosanska Krajina, Tuzla in the northeast and Mostar, the capital of Herzegovina.
Wikipedia's Bosnia & Hercegovina Page
You can find, however, at the same link fairly precise boundaries for the ten cantons that make up the Federation of Bosnia-Hercegovina as well as the seven regions of Republika Srpska.
The Library at U Texas has a map illustrating the boundaries between the two entities, however:
U Texas Bosnia-Hercegovina Map
They don't mesh with the cantons, course.