According to Scott Watanabe, the movie is set in an alternate future where after the 1906 earthquake, San Francisco was rebuilt by Japanese immigrants using techniques that allow movement and flexibility in a seismic event. After the city was finished being rebuilt, it was renamed San Fransokyo due to it being a city with Japanese and American architecture combined.
Baymax's movement and posing was modeled after studying the movement of a baby with a full diaper.
The production team watched videos of fire ants as an inspiration of the movement of the Microbots.
In order to create the thousands of civilians living in San Fransokyo, the production team invented a program called the "Denizen Factory," which allowed them to build a whole series of background characters that each have a distinct design.
When Hiro falls between his desk and bed after activating Baymax, you can see Oswald the Lucky Rabbit's face on Hiro's ceiling. Oswald was Walt Disney's first animated character before Mickey Mouse.