According to screenwriter Bruce Wagner, the casting of Robert Pattinson was what finally got the movie made, financially speaking.
In an almost 50-year career, this was the very first time that David Cronenberg ever filmed anything in the United States (his previous movies were mostly shot in Canada or the UK). The film shot for 5 days in Los Angeles and Beverly Hills (location manager Scott Trimble) and 24 days in Cronenberg's native Toronto (location manager Marty Dejczak).
Novelist and screenwriter Bruce Wagner appears uncredited in Maps to the Stars (2014): He is the bald chauffeur wearing sunglasses and a black suit who's standing in the background as Benjie Weiss is insulting Arnold in front of the L.A. Children's Hospital. Wagner used to work as a chauffeur and limousine driver before becoming famous as a novelist.
As more of Agatha's past is revealed to the viewer, the more visible and pronounced her scar tissue becomes.
The movie was going to be shot in 2004, with David Cronenberg and Julianne Moore already attached to the project, but the director wanted to shoot the film in Los Angeles and it was financially impossible.