In the universe of The Expanse Ganymede has millions of residents and Ganymede Station was one of the first permanent human settlements in the outer planets, built as a long term colony with large domes filled with food crops. Large mirrors were placed around the moon to supply the Sun's light to the surface for crop growth. It was known as the safest station in the Jovian system, and many humans from other colonies traveled to Ganymede to deliver their babies, as the magnetosphere helps claim the Jovian moon the lowest amount of birth defects and stillbirths. Initially, at the start of the series, Ganymede is divided between the United Nations and Mars.
The life on Ganymede is depicted in season 2 of The Expanse. Here you can view some of the best shots from Ganymede (downscaled from 4K UHD screens for better image quality) as well as some concept art for it.
Inside an agricultural dome on Ganymede:
Magnetosphere protects Ganymede from Jupiter's harsh radiation belt:
A ship landing at a human colony on Ganymede:
Concept art for a Ganymede greenhouse by Romain Jouandeau: