On your letter of offer your contracting organisation will be listed either as Oita Prefecture, in which case you are a prefectural level ALT. Or as a specific City within Oita prefecture, in which case you are a city level ALT.
If you are a prefectural ALT, in almost all cases you will be teaching at one or more high schools. City level ALT's will teach primarily at either or both elementary and junior high schools. Although some city placements will also involve kindergartens or academy's (gakuen).