Hogwarts Express Route
As shown, the Hogwarts Express runs down the backstage road connecting the two parks. If there was an elevation showing the track, it would show a system relatively similar to the bus/train things that run through Miami, with the capability of switchable vehicles to allow for easier transfers. The main shutters of the train are normally closed, but when the trains reach the expanded section in the parking lot area, they encounter a Kong 360 esque sequence through some rolling hills either showing Hogwarts at a distance (if the train is traveling from Hogsmeade) or London at a distance (if the train is traveling from London).
London/Diagon Alley (Only "WWoHP - London" on Maps)
The main setting is London, with King's Cross (St. Pancras station, really) being the main weenie of the area with its huge clocktower. The streets are like alleyways in London, facades everywhere, and classical architecture laden with semi-modern accents, and a double-decker. This area operates by itself as a themed area, but it blends through the Leaky Cauldron, where there is a passageway that leads straight towards Diagon Alley. In Diagon, some shops are open, and some are not. Ollivander's is still here even though it's also in Hogsmeade, simply because it's such a popular attraction (at the end of every show, the main speaker references the other shop, which can be accessed by taking the train). Weasley's Wizard Wheezes is another open shop, and guests can explore Knockturn Alley as well. On the other branching streets, boxes for "merchandise" block the way to allow for a forced perspective effect. The main attraction here is the Gringotts Bank tour, which is the huge building above everything else, disguised with a London panoramic to hide it.
Building Comparison
Basically, Gringotts is huge compared to Mummy, so there is plenty of space for intimate moments using the patented moving base, and for the nice coaster segments which are imperative.