Lush tropical rain forest once dominated the landscape. The climate of the island is tropical, hot, and humid. The equator crosses the island at its centre in West Sumatra and Riau provinces. The Bukit Barisan mountains, which contain several active volcanoes, form the backbone of the island, while the northeastern area contains large plains and lowlands with swamps, mangrove forest and complex river systems. The northern tip of Sumatra is near the Andaman Islands, while off the southeastern coast lie the islands of Bangka and Belitung, Karimata Strait and the Java Sea. In the southeast, the narrow Sunda Strait, containing the Krakatoa Archipelago, separates Sumatra from Java. In the northeast, the narrow Strait of Malacca separates the island from the Malay Peninsula, which is an extension of the Eurasian continent. The Indian Ocean borders the northwest, west, and southwest coasts of Sumatra, with the island chain of Simeulue, Nias, Mentawai, and Enggano off the western coast. Sumatra is an elongated landmass spanning a diagonal northwest–southeast axis. 2), including adjacent islands such as the Simeulue, Nias, Mentawai, Enggano, Riau Islands, Bangka Belitung and Krakatoa archipelago.

It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 475,807.63 km 2 (182,812 mi. Sumatra is one of the Sunda Islands of western Indonesia.

Sumatera barat indonesia