Why is themost farming in ancient Egypt and in present day Egypt done along the Nile?

Essentially the rest of Egypt is almost uninhabitable and impossible to live on (except perhaps on the shores of Medditeranean and the Red Sea). This is due to the lack of water there. The area of Nile, however, is quite fertile and can be irrigated from the Nile, which is why it's a good place to live in and farm on!