It’s interesting to consider that Field of Research (FoR) codes are categorised according to the methodology used, not the research activity itself (this can be a bit confusing; after all methods are very diverse in themselves).
The two-digit divisions that are probably most useful are 19 (Studies in Creative Arts and Writing) and 20 (Language, Communication and Culture). Within these divisions we find specific identifiers for digital media, for instance: 1902 Film, Television and Digital Media; and 2001 Communication and Media Studies.
As to how the field is structured more generally, think of colleagues, the people we meet at conferences, and those whose work we cite. Large communication associations like ICA and IAMCR often subscribe to activity categories. In the past “activity descriptors” like mass communication, political economy of the media, intercultural communication, and global media identified most of the research being conducted.
It’s not hard to notice, however, that the field is increasing eclectic. For instance, media and communication studies is now informed and enriched by:
Policy studies (cultural and media/ communications policy)
Science and Technology Studies
Media industry studies/ creative industries
Labour studies (e.g. creative labour)
Business and management (in China, cultural management is a big field)