The Andaman and Nicobar Islands form an arcuate chain that stretches from 6⁰45^/ N to 13⁰45^/N and from 92⁰10^/E to 94⁰15^/E for a distance of about 590 km and a maximum width of about 58 km, and is convex to the west. This archipelago consists of 265 large and small islands with a total size of 8249 square kilometres. There are two main groupings of islands that make up this entire chain. The Ten Degree Channel separates the Great Andaman group of islands in the north from the Nicobar group in the south. The Andaman Sea is made up of roughly 203 islands that are all connected. It is 260 kilometres long and 30 kilometres wide, having a total size of 6596 square kilometres. North Andaman, Middle Andaman, and South Andaman are the three primary groups of islands in this group. Duncan Passage, which is 50 kilometres wide, separates the Little andaman from the Great Andaman.

The Nicobar group of islands consists of seven large and twelve minor islands, as well as a number of small islands. They stretch for 262 kilometres and have a maximum width of 58 kilometres, covering an area of 1,653 square kilometres. The Great Nicobar Island, as its name implies, is the largest, measuring 50 by 25 kilometres. It is Indonesia's southernmost island, only 147 kilometres away from Sumatra.

The majority of these islands are made up of tertiary sandstone, limestone, and shale, with basic and super basic volcanoes as its foundation. North of Port Blair lie the volcanic islands of Barren and Narcondam. Coral reefs line the shores of some of the islands. Many of them are densely forested, and others are deeply dissected. The majority of the islands are hilly and reach significant altitudes. The tallest mountain in North Andaman is Saddle Peak (737 m).