If I were going to suggest a rule for this, I would say that if the degrees west longitude of the origin -plus- the degrees east longitude of the destination is less than 180, then the route is "over the Atlantic." If the sum is more than 180, then the route is "over the Pacific." Thus, LAX to DEL would be "over the Pacific" while ORD to DEL would be "over the Atlantic." Is JFK to SIN considered "over the Atlantic"? It would be under my proposed rule....