This project's reading
Zootopia does not ask anyone to fit one climate. A polar bear does not have to live in the desert to be a citizen. Read as a city of people, the districts look like ethnic enclaves and ethnoburbs: Koreatown, Little Saigon, the Chinese suburbs of the San Gabriel Valley. People keep their language, food, shops and churches close by, and still work, vote and ride the train with everyone else.
The subway map makes the case better than any speech. Every line runs through Downtown or Savanna Central. You can live in your own district and still be one stop from everyone else.
The film also shows the cost. Little Rodentia has a fence, and the fence works both ways: it keeps the smallest animals from being stepped on, and it keeps everyone else out. And the districts only exist because the city runs huge machines to make them. Who built those machines is the question of the sequel.