There's another trick used at Disneyland (I'm not sure about the other parks) is there's very few long lines of sight in the park. The walkways connecting the lands have curves with trees and theme elements blocking your line of sight on the inside of the curve.
The short sight lines help keep everything in view the same theme so you're not jolted out of the "Land" you're in. It also helps keep the park from looking full. A majority of the park's crowd is outside of your line of sight at any given time.
Notice how crowded Main Street or New Orleans Square feels during a show/parade vs five minutes after it's over. You'd think the crowd got bussed out of the park.
It's even cleverer when combined with the forced perspective so the short sight lines never really look short. The forced perspective of nearby buildings tricks you into thinking distant buildings are farther away than they are.
I took the backstage tour at WDW and they were proud to point out that they even balance the background music between lands to create a subtle transition and not jolt you from one theme to the next. Even the placement of walkway and landscaping elements is a gradient from one to the other.
How do they do it, like the imuse system of in mokey island 2, where different music layers get added and removed as you move aeound?
(See https://youtu.be/7N41TEcjcvM)
It's not quite to that level, but they carefully study the acoustics and position all speakers so the transition is gradual and not jarring. They might also choose songs that have elements of both lands to use in areas close to the transition point.
Semi-related: if you go on the Disneyland version of Pirates of the Caribbean, there is a short section of caves right between the first and second drop. The section only lasts maybe 10/15 seconds, but it's where you hear A Pirate's Life for Me for the first time in the entire ride as a kind of foreshadowing of what you will see later. Well, as soon as you go down the second drop, which is not that steep or long, the music is completely gone, and all you can hear is the atmospheric ambient music for the "main" cave section. I always found that incredibly fascinating, since you can turn around and see the previous area, but you cannot hear the music at all.
EDIT: there is actually something that is closer to iMuse, at least the way it was implemented in the Special Edition. Their parade routes are divided into multiple zones, and the soundtrack is equally divided in sections for each float. They use a positioning system to determine where each float is, and feed the correct section of the soundtrack to that speaker zone. It works incredibly well, and you don't notice it at all while you're there.
Each section is basically the same length, the whole thing is (mostly) in the same exact key, of course it's the same BPM across the board, and each section has an intro/outro that can act as transition points to mix into the next section. They can also, of course, loop ad libitum if the parade were to stop for a few minutes. Really cool stuff!
There's another reason that this is done. It's to separate the different copies of the characters. There are multiple of all of them in every park, but by keeping the sight lines contained like this there can be 9 Mickey's all over and you can never see two at the same time.
I took my kids to Disney last year for the first time. We went to go see Anna and Elsa. The line moved fairly quickly, and the group ahead of us went in through a closed door. Almost immediately the door opened again and we were pulled through. Rather than seeing the princesses, we were in a hallway of the house with ~8 doors, and immediately shuffled into one of them where the princesses now were. On the way through, I tongue-in-cheek asked the attendant what was behind the other doors. "Broom closets."
Can confirm, there’s only one Mickey, they time their exits and entrances and have a park coordinator (mostly women under the Mickey costume, by the way, because of costume size categories).
On a related note, if you're ever playing a sandbox game that lets you build and are wondering how to make your builds look better: this is rule number 1. In Minecraft, don't allow for seeing anything further than 20-25 blocks away (which also means very few straight paths). Block the view with anything and your base will magically start feeling much bigger, much more immersive, and become something you actively want to walk around.
Things are also designed so that in Disneyland you cannot see any structure outside of the park (although I think there might be some part where you can see some high-tension power lines). It was a mix of design and strong-arming the zoning commission of Anaheim.
That is a very impressive aspect. After reading about the sight lines at Disneyland however many years ago, I've started actively looking for them when I've visited. It's impressive what you can't see but know must be there (power lines, access tunnels, etc).
The short sight lines help keep everything in view the same theme so you're not jolted out of the "Land" you're in. It also helps keep the park from looking full. A majority of the park's crowd is outside of your line of sight at any given time.
Notice how crowded Main Street or New Orleans Square feels during a show/parade vs five minutes after it's over. You'd think the crowd got bussed out of the park.
It's even cleverer when combined with the forced perspective so the short sight lines never really look short. The forced perspective of nearby buildings tricks you into thinking distant buildings are farther away than they are.