Siayan is one of the Batanes Islands. Also known as Ditarem Island in the native language, the island is about 1/2 mile to 3/4 miles in diameter and lies about 5 miles (8 km) north-northeastward of Itbayat Island. The closest island is Mabudis Island which is about 1¹⁄₂ miles north-northeastward of Siayan.