Hemingway uses the setting as a metaphor for the couple's relationship. What the setting tells us is that, while both parts of the view are part of the same landscape, the parts are are divided from each other. What the metaphor of the setting tells us about the characters is that, while they are a couple and metaphorically part of the same landscape, they are as divided as the landscape. This foreshadows the unwritten outcome of the debate they are having and of their relationship. It also tells us that one individual in the couple represents a position that equates to a landscape with no trees and no shade (but this does not indicate which character this is). It also tells us that the characters have perspectives and precepts that make them like two sets of train tracks going separate ways.
On this side there was no shade and no trees and the station was between two lines of rails in the sun.
Their physical actions display and reinforce their separateness, a characterization that overrides and belies the words they might speak. While saying how he only wants Jig to agree to the "operation" if she wants to, the man goes into the bar alone and has a second Anis (probably without water) alone and watches the other people being "reasonable" while they await the coming train. This, of course, implies that the man perceives Jig as unreasonable.
They were all waiting reasonably for the train. He went out through the bead curtain.
Similarly, when Jig walks to the end of the station to look at the scene and the Ebro, she is demonstrating her separateness from the man. So while she says she is being amused, she is really being driven apart from the man:
'And we could have all this,’ she said. ‘And we could have everything and every day we make it more impossible.’