Pemba is the second largest island in the Zanzibar archipelago, a part of Tanzania, in the Indian Ocean just off mainland Tanzania in East Africa. The largest island is known as Zanzibar by most of the world, but its local name is Unguja. It's about 25 miles directly across the channel from Dar es Salaam, the Tanzanian city on the mainland. Stone Town, the ancient Arab trading city at the heart of Zanzibar City and a World Heritage site, is the center of Unguja's thriving tourism industry. 25 miles north of Unguja is Pemba -- 40 miles long and 15 miles wide, with a population of about 500,000. There's little tourism, and people live mainly by fishing and farming.