Where the shape comes from
A stepped bank of earth seen from the side — the notches were read early on as the footholds cut into a loess slope. On the left of a character it shrinks to 阝 and marks slopes, walls and the ground they stand on: 院 a walled courtyard, 阳 the sunny side of a hill, 阴 the shady side, 除, 陈, 队. Remember which side you are on: 阝 on the left is this mound, 阝 on the right is the city 邑.