Tutoring geography, you notice features on maps.
Apparently, the Dahomey Gap, possibly aka the Togo Gap, is a strip of dry woodland that runs north from the coast of Benin, Togo, and eastern Ghana.
The Gap divides the equatorial rainforest of west Africa into two distinct regions. While no tall mountains surround it, uplands do, which may explain its local dryness.
O’Shea, Mark. Venomous Snakes of the World. Princeton: Princeton University Press, 2005.
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.