Genesis 47:21 - Ellicott's Commentary On The Whole Bible

He removed them to cities. — Joseph’s object in this measure was most merciful. As the corn 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 every year are overflowed by the Nile.