I heard this in the BBC radio and the host and others were talking about some pictures
one said "I like the one where he's on your back"
Why would the relative adverb where be used here? I thought where is supposed to refer to a place?
in this sentence "where" means "In which".
Maybe if you divide the main clause from the relative clause you can understand better:
"I like the picture." "In the picture he's on your back"--> "I like the picture in which he is on your back"--> "I like the picture where he's on your back".
I hope it is clear.