Question

How did the geography of mesopotamia and egypt shape their cultures?

Answer 1

 the Rivers are absolutely essential to understanding these two areas of culture. They both flood annually, providing some guarantee of grain and water, and provide much needed shipping lanes for the civilizations. Both were close to the mediterannean sea, persian gulf and red sea - ideal trading opportunities. 
Egypt is essentially enclosed by desert and sea, making it a nation with natural boundaries. Mesopotamia is similar in that is is bordered by desert to the east and south, mountains to the north and sea to the west. 
Both are quite literally "Cradles of civilization".