Charles Ellicott Commentary Genesis 47:21

"And as for the people, he removed them to the cities from one end of the border of Egypt even to the other end thereof." — Genesis 47:21 (ASV)

He removed them to cities. —Joseph’s object in this measure was most merciful. As the grain was stored up in the cities, the people would be sure of nourishment only if they were in the immediate neighbourhood of the food. As a consequence, possibly, of Joseph’s policy, the number of cities in the Valley of the Nile became so enormous that Herodotus computes them at 20,000. Thus the people would not dwell at any distance from their lands, while it would be impossible for them to reside actually on their plots of ground, as these are flooded by the Nile every year.