The poem takes us to the Sargasso Sea in its first line but then switches to London in its second. This jump between an oceanic to an urban setting occurs throughout "Portrait d'une Femme." We seem to be simultaneously wading through soggy pieces of wood floating on the sea (26) and observing conversations taking place in an ornately decorated living room (22). This is how we get both ambergris, which comes from whale intestines, and "rare inlays," which usually decorate jars and wooden furniture, all at once in line 23.
The first line, in which the woman is specifically identified as "our Sargasso Sea" (1), suggests that London may be the actual, broader setting for the poem, the place where both the speaker and the woman interact, while the sea may be a metaphor for the woman's personality. In other words, rather than being a distinctive, substantial character, the woman is more like a space that collects various experiences and impressions that are projected onto her by other people (the speaker included), just like the Sargasso Sea collects sodden wood and other "fished up" trophies (16).