Sumatra was an island in the south Pacific Ocean.
The Second Doctor, Jamie McCrimmon and Victoria Waterfield visited a post-21st century Sumatra. (AUDIO: The Great Space Elevator)
On the same day as the volcanic eruption of Krakatoa in 1883, a sketch of the Ninth Doctor washed up on a beach on Sumatra. It eventually found its way into Clive Finch's collection of artefacts related to the Doctor. (TV: Rose)
In the late 19th century, Silas Beckett told Vastra and Jenny Flint that he was saved from an attack in Millwall by a Sumatran man. Jenny doubted this. (AUDIO: The Cars That Ate London!)