Splatoon 2 has a good variety of maps to go around across a variety of modes, so players won't get bored by the territory that they'll be able to paint over. That said, there is a special one being planned that will only be available during one particular type of event – the Splatfest.
Nintendo has revealed that a new map will be introduced only during these events, in the form of the Shifty Station. What's more, it won't stay the same each time it's introduced, as the publisher has noted that it will change with each Splatfest, possibly to throw players off as they attempt to plan strategies for covering it with their paint.
Nintendo didn't give a reason as to why the map was only being offered during Splatfests, but more than likely it has to do with drawing players in to the game at specific times. That, and maybe trying to see how it fares before permanently adding it to the roster, which is always a possibility. Nintendo has noted that DLC for the game will be free, and the Station could very well be a part of it somewhere down the road.
For now, though, the Splatfest is the place where you can find it, and the next one will unfold this weekend, starting at 9 PM PDT on August 4th and going for a full 24 hours. It's a good opportunity to jump in and see what the map is all about, while competing against the vast majority of the Splatoon community.