Jamieson, Fausset and Brown on Jeremiah 47:5

5. Baldness ... cut thyself--Palestine is represented as a female who has torn off her hair and cut her flesh, the heathenish (Le 19:28) token of mourning (Jr 48:37).

their valley--the long strip of low plain occupied by the Philistines along the Mediterranean, west of the mountains of Judea. The Septuagint reads Anakim, the remains of whom were settled in those regions (Nu 13:28). Joshua dislodged them so that none were left but in Gaza, Gath, and Ashdod (Jos 11:21, 22). But the parallel (Jr 47:7), "Ashkelon ... the sea-shore," established English Version here, "Ashkelon ... their valley."