John sees four angels, each standing at a corner of the earth. Given that the earth is round, we realize the language is metaphorical. This is not strange language, however, because we also speak of four directions, all reaching to the “corners” of the earth farthest removed from the place we live.
1 After this I saw four angels standing at the four corners of the earth, holding back the four winds of the earth, that no wind might blow on earth or sea or against any tree.