Just wanted to add a few comments about how the elevated railway going over Diagon Alley fits in with the theme. The Wizarding World of Harry Potter is a very faithful embodiment of the books and films, but obviously is not 100% identical to them. They've already taken some creative license in the past to make everything work in a theme park context. For example, the presence of Ollivander's Wand Shop in Hogsmeade Village does not exist in the books or films, but the story in the park is that a second location has been opened in Hogsmeade. This was so the Ollivander's concept could be included in the experience before Diagon Alley ever existed at Universal. While Universal has changed/added/created things that are different from what we see in the films or read in the books, they've made these alterations with the utmost care and creativity, so they don't really clash with the world we see on the screen or page. Actually, the films display subtle changes from film to film as well (just look how the castle and its setting change and adapt throughout the series as the tone of the films change or as the plot requires.) The great thing about all of this is that The Wizarding World perfectly lends itself to these changes/additions/adaptations, because, well, simple magic can explain away the sudden appearance of an elevated railway zooming over Diagon Alley.