[1] "That picture was taken in the park where I used to play." (Here, 'where' is an relative adverb.
[2] "I remember the day when we first met." (Here, 'when' is an relative adverb.)
Source : https://www.ef.com/ca/english-resources/english-grammar/relative-adverbs/
[3] "Grandma remembers a time when radio shows were popular." (Here, 'when' is a relative pronoun.)
[4] "I want to visit the island where my grandma was born." (Here, 'where' is a relative pronoun.)
Source : https://grammar.yourdictionary.com/parts-of-speech/pronouns/relative-pronoun.html
It seems to be confusing that "when" and "where" are relative adverbs in sentence [1] & [2] while they're relative pronouns in sentence [3] and [4].
How can we determine whether "when" and "where" are relativel pronouns or relative adverbs?