Categories are often placed in several other categories  See WikipediaCategorization for more info on categories  As far as the convention yes it has been what weve been doing  Its done at every nationalitys hip hop groups categorySee CategoryHip hop groups by nationality  The reason we do it this way is so that someone can be looking at CategoryHong Kong hip hop then head over to CategoryHong Kong hip hop musicians and then choose between rappers and groups  Makes navigation better  Peace