Both facets of fiction depict an ultra-realistic or deeply unrealistic setting, albeit display factual elements and messages for which one living in the "real world" can relate to (author's note). Both take place in a world that could resemble the world we live in, but in an unrealistic manner. Dystopian fiction generally focuses on the location as it's science fiction-esque essence, but science fiction is more of a broader term.
EDIT: Both are used to describe a genre of fiction.
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