Malaysia lies at the heart of South East Asia and is made up of the mainland and Borneo Island. Peninsular Malaysia has a land frontier with Thailand in the North. In the South, it is linked to Singapore by a causeway. To the West, across the Straits of Melaka, lies the Indonesian Island of Sumatra. The Philippine Islands lie to the North-east of Sabah. There are two regions separated by the South China Sea: Peninsular Malaysia extending from Kra Isthmus to the Straits of Johor, and Sabah and Sarawak on the North-western coast of the island of Borneo. Primary forests cover 60 percent of Malaysia and contain a variety of lush and tropical vegetation. The country is subjected to maritime influences and the interplay of wind systems, which originate in the Indian Ocean and the South China Sea. The climate is tropical and humidity is high due to rainfall.