What is the meaning of "El Gevul Edom"?
Rashi: It is near the border of Edom. Malbim
Why does it say "mi'Ketzei Teiman"?
Rashi: That was the end of the border. (I.e. Midbar Tzin did not span the entire southern border, rather, only at Teiman - Radak, Metzudas David.)