Sodden was a former kingdom located around the Yaruga river between Cintra, Brugge, and Riverdell. In the aftermath of the First Nilfgaard War, Sodden was split between Nilfgaard and the Northern Kingdoms into Upper Sodden and Lower Sodden. However, with the Peace of Cintra, the two halves were recombined into Sodden and it became a vassal state of Temeria.
The coat of arms for Sodden is not actually described in the novels. This particular coat of arms was designed by our resident heraldry and Witcher expert Mboro and was considered unofficial until they were used in The Witcher 3: Wild Hunt as part of Ciri's family tree image.