Mark Strand's poem "Keeping Things Whole" is a philosophical or reflective poem concerning man's relationship to his environment, to the space around him. The only setting mentioned is that of a field. And yet, there are no descriptive words for this setting. If you look up "field" in the dictionary, you will find 11 different meanings for field. These range from a playing field, farmland, a military setting, a background for an object, etc. "Field" can apply to sports, the military, art, agriculture, physics, electricity, photography, and any of these particular meanings work well in the poem.
The speaker defines himself as being apart from his environment, his field, his surrounding space. When he moves, he creates an absence of whatever occupied the space before him. In the second part of the poem, Strand replaces "field" with "air" that occupied the space before the speaker occupied it and that occupies it once he moves out of the space.
This lack of detail is important. The fact that no details identifying the type of field keeps us from identifying one particular setting with the poem's meaning. All we do know is that the speaker feels as if he is a negative influence on his environment, that where he is, things are not united and that when he moves, things become whole again. He desires to keep things whole, and only his moving will do that. In this way, we can broaden the meaning of field even more to that of human relationships, that possibly the speaker feels that his absence contributes more than does his presence.
So, if I had to answer this question, I would focus on the speaker's relationship to his setting--how he feels about his presence and absence in it, and how that meaning is conveyed.