This poem doesn't take place at a specified location or time. Instead, it’s meant to be viewed in relation to the speaker (or, by extension, the reader). It takes place in the late years of the speaker’s life as their mental state is beginning to deteriorate. It’s a transitional phase in which the speaker still has an awareness of the things they once took for granted — mathematical equations, geography, world culture. They haven’t quite lost themselves yet, and so they’re aware of the broadening holes. By the end of the poem, it’s implied that the speaker will soon be losing themselves completely.