Horizon is the second piece of navigation: what can I realistically see from here? It matters because a person’s choices are bounded by the futures they know exist — you cannot orient toward a world you have never encountered. So horizon is not a fixed given but something the model actively enlarges, on a real developmental commitment:
No participant should have their imaginable future unnecessarily confined by the accident of their immediate field.
Travel is only one old technology for widening it; books, education, art, science, cross-cultural contact, mentors, and unfamiliar communities all change the accessible view. This is what horizon infrastructure provides, and its deepest purpose is a single protection — your present field should not be allowed to masquerade as the total field — which guards against tribal enclosure. At civilizational scale, horizon breadth — how many substantively different viable futures a society can perceive — is a measure of how brittle or resilient it is. See Navigability.