Some wonders and districts can only be built on certain types of terrain. By expanding your city out in this manner, Civ VI also forces you to pay more attention to the map and where to place cities and structures. It’s somewhat similar to how Endless Legend did it some years ago. If you want to build temples and religious buildings, you have to have a religious district and if you want defensive and military stuff you need a district for that.
While the previous games mostly dealt with a single tile that housed your entire population, Civ VI has you building out in different districts.
Civilization VI’s main new thing is a reworked model for how you build out your cities. Civilization IV had religion and culture play a large part and V tried to streamline and clarify the gameplay and adding the city-state system which gave you other allies and enemies besides the core cultures.
Over the years, each new game in the series has tried to nudge or switch up the formula while keeping to the core of what makes it special. Of course, they have all had shortcomings but the core is still strong enough to lure me back into its warm time-murdering embrace, again and again. There is just something wholesome and satisfying about taking one of several civilizations and guide them through a condensed version of history, dealing with human issues like feeding people in deserts, finding iron and other resources and avoid getting nuked by Gandhi. I must have poured thousands of hours into the Civilization franchise in total.