Nii-jima (新島) is located in the northern Izu-shotō, situated between the small islands of To-shima and Kōzu-shima; To-shima lies 9 km to the north and Kōzu-shima 14 km to northeast. Izu Ōshima, the largest and most populous of the Izu-shotō lies 30 km to the north.

Nii-jima (23.8 km²) is unusual amongst the islands of the Izu-shotō group in that it has an elongate outline — the island measures 11 km in length (north to south) with a maximum width of 3 km occurring across the island's southern section.

The island has three main topographic units: two steep-sided, flat-topped domes (one each in the north and south) that are joined by a low-lying plain in the centre. The larger northern plateau region, constructed from several smaller rhyolitic lava domes, stands considerably taller than its southern counterpart and contains the island's highest elevation of 432 m above sea level at Miyatsuka-yama. The southern dome reaches 283 m above sea level at the summit of Tango-yama. Rhyolite lavas and their erosional and decomposition products give the island its famed white cliffs and white sandy beaches, including the 6.5 km long Habushi Beach on the east coast and the 4 km long Maehama Beach on the west coast.

Nii-jima has several offshore islets, including Jinai-jima off the southwest coast and Haya-jima off the southeast corner. 2.5 km off the southwestern tip of Nii-jima (and partly visible at the bottom left corner of the above image) is the neighbouring island of Shikine-jima.

image: ASTER volcano archive jpl/nasa