Where the shape comes from
A wall 囗 above a kneeling figure: the boundary and the people living inside it. Squeezed against the right edge of a character it becomes 阝, and it names places and the administration of places: 都 a capital and then "all", 部 a department, 邮 the post, 郊 the outskirts, 那, 邻. Its twin trap: the identical 阝 on the *left* is not this radical but the mound 阜.