Sets up a hypothetical so you can talk it through: 우리가 전라남도 쪽을 간다고 쳐요 "say we head down toward Jeollanam-do", 둘이 만난다고 치면 "supposing the two of them meet". Every line here is that — a speaker building an example before explaining something, twice introduced by 예를 들어서 "for instance". 치다 has nothing to do with hitting here; it means "count it as", "treat it as true for now".