The red icons on the map denote the exotic locales that Frank mentions during his pseudo-courtship of Eveline, while the green icon is placed at the North Wall of the river port in Dublin. Although she imagines exploring wildly distant places, she is ultimately paralysed on the North Wall while she watches Frank depart.
While working on the map, it was notable that while each of the locations she imagines exploring with Frank involves increasingly significant distances, the actual location of Liverpool (where he is likely actually taking her) fits under the same large green icon as the North Wall when you are zoomed out far enough to see distant Buenos Aires. A key element of the story seems to be the ephemeral or imaginary status of these exotic locations that are associated with the ocean and Frank's occupation as a sailor. Eveline's dissociation at the end of the story leaves these imaginary places as unreal and unexplored, as intangible and fluctuating as the ocean and her theoretical future with Frank.