The term "Shephelah" means the "lowland" and appears in the Hebrew Bible 20 times. It is a long rectangular area of soft limestone (Eocene) stretching from Gezer in the north to just north of Beersheba in the south. It is about 27 mi. [43 km.] long and 10 mi [16 km.] wide. In a sense, it is the area of foothills that separate the Philistine Plain to the west from the Hill Country of Judah to the east — a "buffer zone."
See the Zondervan Atlas of the Bible pp. 52-54 for a detailed description of the Shephelah.