Does anybody knows why we use the term "west power" (barat daya) for Southwest ? Looking at the Indonesian archipelago on a map, I think I understand why Northeast is "east sea" (timur laut), but where does the term "power" come from ? Is it related to the power of the Indian ocean there, bringing storms and occasionally tsunamis? Or is it related to the power of Java Island and Jakarta, located on the southwest of the archipelago ?
'Daya' in this context does not mean power. Austronesian languages including Indonesian originally use the land-sea axis and monsoon (wind) axis to form directions. In Proto-Austronesian, the ancestor language of all Austronesian languages, Lahud (Indonesian ‘laut’) and Daya means seawards and inland respectively. Because of that, relative to the location of the speaker of a particular Austronesian language, these words would correspond to different cardinal directions e.g. ‘Daya’ in Ilocano (North Philippines) means east while ‘Daya’ in Puyuma (Taiwan) means west. In Indonesian however, ‘Daya’ is only seen in ‘Barat daya’ (Southwest) possibly indicating that the direction of the land relative to the people who constructed the term may be towards the southwest and have the sea to their northeast. https://en.wikipedia.org/wiki/Proto-Austronesian_language#Colors_and_directions