Great Nicobar, the southernmost island of the Nicobar Islands in India, is located in the Andaman Sea. Sumatra, an island in Indonesia, lies to the south of Great Nicobar, making it the closest large landmass. This proximity is significant in the context of geographical studies, as it highlights the tectonic interactions and biological connections between India and Southeast Asia, which are relevant topics in both physical geography and ecological studies covered in UPSC GS Paper I examinations.