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.
Although it is based on a Marvel comic of the same name, there are lots of changes to the names, the setting, the ethnicities of characters, the back stories, and several plot points.