Brad Bird takes us behind the scenes of Ray Gunns massive sci-fi city

The first character you meet in Brad Bird's Ray Gunn isn't the titular private eye (voiced by Sam Rockwell).

Nor is it his alien colleague, Eyera (voiced by Tom Waits), nor even pop superstar Venus Nova (voiced by Scarlett Johansson).

Instead, it's the film's setting: the massive, retro-futuristic city of Metropia.

Ray Gunn 's opening sequence zips viewers through the canyons between Metropia's mile-high buildings.

Flying cars and elevated trains transport hordes of humans and aliens alike, but commuters could just as easily rent a jetpack for quick travel.

For them, it's business as usual, but for viewers, it's a rollicking introduction to an astounding city.

SEE ALSO: How 'Ray Gunn's Venus Nova, pop star of the (retro) future, evolved Bird has been working to make Ray Gunn since the '90s, and he's stressed Metropia's importance from the very beginning.

In an introductory note on a script draft from 1996, he wrote that the one character he couldn't adequately capture on the page was Metropia.

In this world, he wrote, "Cities are gargantuan jewels that stretch into the heavens." As Ray Gunn moved from page to screen, how did Bird and his team manage to bring the jewel of Metropia to life? At a press day at Netflix's animation studios, Bird and his collaborators broke down the influences and techniques behind the finished version of Metropia, as well as the importance of getting it right.

"The movie took place almost entirely in that city, and if the city wasn't a character, it would be an empty experience," Bird told Mashable.

According to Ray Gun art director Wendell Luebbe, Bird wanted to combine two different styles for the look of Metropia.

One was the work of early 20th century architect Hugh Ferriss, who dreamed up tall, stepped buildings. (Fittingly for Ray Gunn , he also wrote the 1929 book The Metropolis of Tomorrow .) The other was Streamline Moderne, a sleeker take on Art Deco that took off during the 1930s.

While Ferriss' work is defined by height and blocky geometry, Streamline Moderne is all about curves and aerodynamics.

Concept art for the city of Metropia.