There are two main settings in this poem: the setting of the house and the neighborhood that the speaker inhabits, waiting for her husband, and then there's the landscape that the speaker's husband journeys through.
The setting of "Changgan"—the ancient Chinese city where the speaker first meets her husband as a little kid, and where she still lives—is familiar and comfortable. It's home. But the setting that the speaker's husband moves through is dangerous. The speaker says that his "long journey" takes him "[t]hrough the Gorges of Ch'u-t'ang, of rock and whirling water." Just by the description of these gorges (near the Yangtze River in China), we get a sense of danger. He'll have to watch his step around those rocks and whirling water.
In the final stanza, the speaker also refers to meeting her husband at "Chang-feng Sha." This is an area that's a few hundred miles away from Changgan. The poem evokes a lot of geography for us. We get names of towns and gorges and cities. This emphasis on geography highlights the speaker's plight. She's sad because she is separated from her hubby by geography.
So, our setting delivers both a sense of comfort and familiarity (the speaker's home turf that she shares with her hubby) and a sense of distance and isolation (dude's on another part of the map, altogether).