Geography . Indonesia is an archipelago in Southeast Asia consisting of 17,000 islands (6,000 inhabited) and straddling the equator. The largest islands are Sumatra, Java (the most populous), Bali, Kalimantan (Indonesia’s part of Borneo), Sulawesi (Celebes), the Nusa Tenggara islands, the Moluccas Islands, and Irian Jaya (also called West Papua), the western part of New Guinea.