Those who know me know that I love Post-Apocalyptic stories. I also like the odd Sci-Fi, but it's the Post-Apoc I'm in love with. Post-Apoc stories, however, can be very hard to find. Publishers/retailers usually don't separate them from Sci-Fi/Fantasy.
First off, Sci-Fi and Fantasy just don't belong together as a genre. They very rarely bleed into each other. If there's a magical element in Sci-Fi, it's usually because of aliens, genetic enhancement, radioactive infection and whatnot. Sci-Fi almost always takes place in the future whereas Fantasy (kingdoms, elves, dwarves, dragson etc.) almost always take place in the "past" (or it's built upon Medieval times with very little modern or futuristic technology at hand). I assume the two were put together in one genre for being "otherworldly". Although this may have been the original reason when Sci-Fi and Fantasy were relatively new in literature, there are thousands upon thousands of each available today, so it's high time to separate the two. Lord of the Rings and Star Trek is NOT the same genre.
A good example of a Sci-Fi is A Solid Core of Alpha by Amy Lane that happens in space, with holograms, space station and space travel. There are no aliens, but aliens aren't a must in Sci-Fi. A good example of Fantasy is Scorpion by Aleksandr Voinov that happens in a world that has never been our Earth, and yet it doesn't happen in space. There aren't any magical elements, which shows that Fantasy doesn't have to be about magic, but it has different sets of rules and kingdoms. A more traditional Fantasy with an elven kingdom among other things is Counterpoint by Rachel Haimowitz.
What I understand a little better is why Sci-Fi and Post-Apoc are thrown together. Both usually take place in the future. However, there's usually a difference. While the two may bleed into each other, mixing a ruined earth with space travel, Sci-Fi usually happens in space while Post-Apoc almost always focuses on Earth after a catastrophe. There may be scientific elements in Post-Apoc, but if it's a story about people on Earth struggling to live in an environment with very changed set of social rules, it's Post-Apoc (also often known as Dystopia). At least these are my definitions.
Post-Apoc and Dystopia are very often the one and same. However, they can be different. Post-Apoc can take place thousands of years after most of humanity died and there's a new and better world. That's not a Dystopia. Dystopia is when the social rules or living conditions are negative (Dystopia is the opposite of Utopia).
A good example of a Post-Apoc is 18% Grey by Anne Tenino where the USA has been split in half after a war, one half being accepting of GLBT; the other not (there are more differences, basically the more accepting one is more technologically advanced while the other half is deteriorating). The story has technological advancements, but it's not Sci-Fi per say, since it's just further development of our technology and not something as big as time travel or warp speed. Another is Marked Yours (Sentries series) by Elizabeth Noble, where the Earth got ruined with volcanic eruptions that killed and destroyed. The USA is split into new parts, one of which has a tradition of master/slave relationships. This is a very thought-out world Noble has crated, but instead of being technologically advanced, it's reverted back to old times with horses and such. It has paranormal elements, but that's Paranormal, not Sci-Fi, so it's a Post-Apocalyptic Dystopia/Paranormal.
Since I'm on the topic, Alternate Universe is not the same as Sci-Fi, Fantasy, Post-Apoc, or Dystopia. Alternate Universe is when something happened in our time, on our planet, that has changed something so dramatically so that our world today is different. It's also known as parallel universe. Characters are living in a world today after the Soviet Union won the Cold War back in the 1990's, or the Chinese took over the world in the 1800's and the world language is Chinese and everyone lives differently, or Kennedy was never assassinated. World hunger was resolved a hundred years ago - the world would be different today if it was.
A good example of an Alternate Universe is The Starving Years by Jordan Castillo Price, where world hunger ended in 1960.
Then what about Fantasy vs. Paranormal vs. Urban Fantasy? Generally, Fantasy takes place in a made-up kingdom, with kings, knights, dragons, elves, and whatever other things a fantasy kingdom needs. Paranormal takes place in our world, usually in our time. Those are vampires, werewolves, fey, angels, etc. Urban Fantasy vs. Paranormal is more difficult to differentiate, and I kind of think people are splitting hairs with this one (kind of like separating Dystopia and Post-Apoc), but a definition I heard while I was still reading YA Paranormal was that Urban Fantasy was basically Paranormal, only it happened in cities. I don't know if that's the correct definition, but it's what I heard.
A classic example of a Paranormal is Rules are Meant to be Broken by N.J. Nielsen, a book about vampires. A good example of Urban Fantasy would be Ink by Isabelle Rowan, about a demon in the city of Melbourne, Australia. (Both of these take place in Australia, actually, but there's no big city backdrop in Rules are Meant to be Broken).
It really bothers me to have to go through Fantasy titles when I'm looking for Sci-Fi. It also bothers me to have to go through Sci-Fi titles to find Post-Apocalyptic. Come on, retailers and publishers, make it easier for us to find the books we want.
I was lucky to stumble upon a list on Goodreads called Gay Post-Apocalyptic/Dystopic. I'm currently working my way through the titles there, but if there's a new Post-Apoc book out? I'll have to wait for it to hit that list, because I won't be able to find it on the retailer sites under a Post-Apoc listing.