East Malaysia is 50% bigger than Peninsular Malaysia at , comparable with South Dakota or Great Britain. East Malaysia contains the five highest mountains in Malaysia, the highest being Mount Kinabalu at 4095 m, which is also the highest mountain in Borneo and the 10th highest mountain peak in Southeast Asia. It also contains the two longest rivers in Malaysia – Rajang River and Kinabatangan River. Banggi Island in Sabah and Bruit Island in Sarawak are the two largest islands that are located entirely within Malaysia. The largest island is Borneo, which is shared with Indonesia and Brunei. The second largest island
Indonesia–Malaysia border the area. The dispute started with Malaysia issuing a map in 1979 of its territorial sea and continental shelf which included the Ambalat block. The map drew Malaysia's maritime boundary in a southeast direction into the Celebes Sea after it leaves the eastmost point on land on Sebatik island. This would include the Ambalat block, or a large part of it, within the Malaysian continental shelf. Indonesia has, like the other neighbours of Malaysia, objected to the map. Indonesia has never officially announced the exact locations of its maritime boundaries but claimed during its arguments in the Sipadan Case that