Simplify the following text for a Grade 20 native English-speaking person.
Original: The borders of Salland are not well defined , but the largest area which may be indicated by Salland , corresponding to the historical dominion , is bound to the west by the provincial border with Gelderland , which is partly formed by river IJssel ; to the north by the Meppelerdiep stream and the provincial border with Drente , which partly consists of the Reest stream ; to the east by the borders with the German state of Lower Saxony and the eastern Overijssel region of Twente ; and to the south by the border with the Gelderland region of Achterhoek , part of which is formed by the Schipbeek stream , with other words Salland is all of Overijssel with the exception of Twente and the region known in Dutch as `` Kop van Overijssel '' .
Simplified: Salland is bound to the west by the provincial border with Gelderland , which is partly formed by river IJssel ; to the north by the Meppelerdiep stream and the provincial border with Drenthe , which partly consists of the Reest stream ; to the east by the borders with the German state of Lower Saxony and the eastern Overijssel region of Twente ; and to the south by the border with the Gelderland region of Achterhoek , part of which is formed by the Schipbeek stream .