Irony of the Rastaman
At first glance, the rastaman might look like an uneducated, superstitious island native: he proposes a worldview that is directly at odds with that of the educated European world, and he himself is Jamaican. Ironically, that is not at all the case; the rastaman actually has a PhD in English Literature from the University of Glasgow, and he has thoroughly examined all the European philosophies before returning to that of his homeland.
Irony of the Cartographer's Objectivity
The cartographer claims that his craft is completely objective, merely recording physical measurements of the land. Ironically, he soon discovers that this is not the case; even his subconscious conceptions and desires concerning the land's appearance on the map influence his subjective judgments, so cartography is not merely an objective science, but also a subjective art.
Irony of Jah
"Jah" is Jamaican patois for "God," who is generally seen as highly intentional and loving in his detailed creation of the world and of man. Ironically, the Jamaican conception of Jah is completely different: he created the world with an indifferent shrug without even really thinking about it first. The contrast between these Gods has a significant impact on each respective religion, explaining some of the major differences between them.
Irony of Zion
The cartographer believes Zion is an actual geographical place. Accordingly, he maps the unexplored parts of the world, but he is never able to find it. Ironically, it's because Zion isn't a place at all, despite Biblical imagery: it's a state of being afforded to those who live according to its principles.
Irony of the Horizon
In the poem "xii. in which the rastaman begins to feel uncomfortable," the cartographer and the rastaman come across a beautiful, expansive view of the horizon and the sea. The cartographer is delighted, but, ironically, the rastaman becomes uncomfortable in the face of such beauty. He thinks such beauty is merely a temptation to leave one's home and go searching for something you will never find on earth.
