The major shipping routes of the South China Sea (SCS) and northern Indian Ocean (NIO) are analyzed via ship observations compiled by the International Comprehensive Ocean-Atmosphere Data Set. In the SCS, one route from the East China Sea moves through the Taiwan Strait toward Hong Kong and Singapore. The other route from the Pacific moves passed the east coast of Taiwan and through the Bashi Channel/Luzon Strait to Singapore. After Singapore, the shipping routes pass through the Strait of Malacca to Sri Lanka. In the Arabian Sea, ships from Sri Lanka go either northwestward toward the Persian Gulf or westward toward the Red Sea. A northeast-southwest route connects the Persian Gulf and the Red Sea. The resultant routes exhibit a triangular pattern in the Arabian Sea. Monsoonal influences on shipping routes are evident in the Arabian Sea, but indiscernible in the SCS. In summer, the southwest monsoon causes strong winds and waves over the western-central Arabian Sea. Ships detour from the southern side of Socotra Island to the northern side. The northern side is on the leeside of the intruding southwesterly flows and has weaker winds and waves than the windward southern side. In the SCS, the winter northeasterly flows intensify winds and waves over two strait regions: the Taiwan Strait and the Luzon Strait. These straits are at the conjunction of the Pacific and the SCS. Routes passing through these straits have the advantage of a short, straight navigation path. Moreover, the winds and waves over these regions are not as strong as those occurring in the Arabian Sea during summer. The maritime conditions in the SCS are not dangerous enough to necessitate a detour.