A shame this thread is so dead. Anyways, I tried to make a comprehensive map of our findings.
The “Sky Tree” can be seen from Inkopolis Plaza. Arowana Mall has this tower basically next door to it. The tower can be seen between buildings across the water on Blackbelly Skatepark. The Sky Tree could also be seen from The Reef, but after the renovation, not anymore. However, it's still visible from The Reef in Octo Canyon.
From The Reef, a Ferris wheel can be seen. This Ferris wheel can be seen on Manta Maria and from Hammerhead Bridge.
During Splatfests, on Hammerhead bridge, fireworks can be seen above an island that is connected with a bridge to the Ferris Wheel. This might actually be where Skipper Pavilion is located since fireworks can be seen very close there. Skipper Pavilion also has a view on two cityscapes that are connected by a bridge. This bridge could be Hammerhead Bridge.
Fireworks can also be seen on Blackbelly Skatepark, but in the distant, even behind the Sky Tree. This might actually be where New Albacore Hotel is located since it has fireworks explode very close to it. Also on New Albacore Hotel, water is just visible around the buildings on team Bravo’s spawn, which means Arowana Mall is located between Blackbelly Skatepark and New Albacore Hotel
From Inkopolis Square, the Inkopolis Tower is visible. It’s said in an interview that from Square, it is a 20-minute walk to Plaza. From Square, a hanging monorail can be seen behind the Deca Tower. The same monorail can be seen in The Reef. They must be close to each other.
From Inkopolis Plaza, another Ferris wheel is visible. This one does not look like the one seen on The Reef, but does look a lot like the one in Wahoo World. If that’s Wahoo World, that means that Blackbelly Skatepark is between Arowana Mall and Wahoo World.
The Inkopolis Tower is visible from Octo Valley.