The main physical characteristic affecting North Africa and Southwest Asia's settlement patterns is water.
<u>Explanation:</u>
The northern part of the continent of Africa and the southwestern part of Asia are predominantly deserts characterized by scarcity of water.
These two regions of the world are counted among the driest on the planet.
Desertification due to rapid deforestation in the past caused these regions to turn into huge sandy deserts.
The countries in the southwest Asia are comparatively wealthy and have been implementing various techniques of desalination of seawater to tackle the scarcity of water in the region.
I would say that the main problem affecting North Africa and SW Asia would most likely be water or the scarcity of it assuming that North Africa would include places like the Sahara Desert and also the south of India which I believe is quite arid..
