The only known map showing the Systres
The Systres are a group of three large islands in the Abecean Sea, far to the southwest of Hammerfell and northwest of Summerset Isle. The nearest islands are Pankor to the northwest and Eyevea to the southeast.
The coral kingdoms of Thras are described as a set of islands southwest of the Chain, which would place the Systres as being near Thras or may mean that the Systres are part of Thras. However, neither explanation has been confirmed, and other sources place Thras as being in the Sea of Pearls instead of the Abecean Sea.