Preston Dunagan used the Unreal Engine 4 to recreate all the areas outside the Kanto region in Pokemon. The model was based on a 1:1 recreation of the world from the original games by counting each step and redesigning every single metric pixel in a 3D model.
Comic Book.com notes that the Kanto region is based on the real life Kanto in Japan. They also note that the Vermillion City is based on Yokohama, while both Saffron City and Celadon City are representations of Tokyo. The Japanese cities get a lot of love in the Pokemon series. You can see how Kanto looks with the flyover video running in the Unreal Engine 4 below.
The video is rife with LOD pop-in, some slight discoloration in one segment, and some optimization issues. Almost all of the shadows stream in seconds late and render just in time to leave the screen. It's tragically funny.
Nevertheless, the Unreal Engine 4 has never been a good go-to source for really large scale, open-world projects due to it being very taxing on the system. Take-Two's RAGE is probably the best on the market right now when it comes to open-world optimization for streaming, flyovers and having a very high-end pipeline for rendering top notch lighting, shadows, entities and effects up close and far away with very few hiccups.
I imagine in this case Dunagan likely didn't make low-end level of detail buildings and objects, which is possibly the cause of the performance lag. Even still, it's an impressive feat and the whole project took him more than seven months and 600 hours to complete.
The flyover covers so many different iconic locations from the Pokemon game, and this is due to Dunagan white-boxing every single step before crafting the rest of the world. He plotted out walking around in the world of the Pokemon games to get an idea how large the game world is, how the map should be designed, and getting the measurements to ensure that the Unreal Engine 4 version would be a 1:1 representation of world that Game Freak crafted for the popular Nintendo handhelds.
This isn't the first time (and it certainly won't be the last) that we've seen popular Nintendo properties recreated in the Unreal Engine 4. Due to Epic's open distribution of the engine and some keen gamers and designers' interest in ripping models from Nintendo properties, we've seen the likes of Link from the Legend of Zelda recreated in the Unreal Engine, along with playable versions of Super Mario and Kirby. Heck, there have even been some renders of various Pokemon running around in a demo map within Epic's game engine.
Dunagan will likely use his new viral video as a resume builder, especially given that he showcases some knowledge of Autodesk Maya and Photoshop, both of which were used to help bring Kanto to life in the video above. This comes just in time as part of the celebration of Pokemon's 20th anniversary.