From The Verge article:
"cities can now expand across multiple tiles, and where you place them is now of greater importance. The key to this is districts, important sections of a city that now take up their own tile. A campus district, for example, will be home to all science buildings, so you can’t build a library or research lab until you have the right district."
Someone needs to call up Sid and friends and remind them that the Civ series is a civilization building game, not a city building game...
Furthermore, you have to build districts in order to have certain buildings. That is just ridiculous. Heck, even city builders don't require you designate districts. That's just micromanagement going in a bad direction.