Sumatra is the sixth largest island in the world (approximately 470,000 km?) and is the largest island entirely in Indonesia (two larger islands, Borneo and New Guinea, are partially in Indonesia).

Sumatra is not very densely populated, about 96 people per km??more than 45 million people in total. It is nonetheless the fifth most populous island in the world. The most populous regions include most of North Sumatra and central highlands in West Sumatra, while the major urban centers are Medan and Palembang.

The people comprise many different ethnic groups, speaking 52 different languages. Most of these groups, however, share many similar traditions and the different tongues are closely related. Malay-speaking people dominate the eastern coast, while people in the southern and central interior speak languages related to Malay, such as the Lampung and Minangkabau people. The highland of northern Sumatra is inhabited by the Bataks, while the northernmost coast is dominated by Acehs. Ethnic Chinese minorities are also present in urban centers.

The majority of people in Sumatra are Muslims (87%), while 10% are Christians, 2% are Buddhist and 1% Hindu.  Most central Bataks are Protestant Christians.

Samosir, or Pulau Samosir, is a large volcanic island in Lake Toba. Lake Toba is located in the north of the island of Sumatra in Indonesia.

The lake and island were formed after the eruption of a super volcano some 75 000 years ago. The island was originally connected to the surrounding caldera wall by a small isthmus, which was cut through to aid navigation.

At 630km?, Samosir is also notable as being the largest island within an island, and the fifth largest lake island in the world.  The island is the centre of the Batak culture and many of this people's artifacts remain on Samosir Island. Lake Toba is the largest and deepest crater lake in world. 906 meters above sea level, a water surface area of 1,265 square km, 90 km long with a coastline of 285 km, and with an average depth of 450 meters. Samosir island is the home of Batak people. The population of Samosir Island is approximately 130.568, or 91 per square kilometer