The biggest and most developed city in Sumatra is Medan. The Arabica from Sidikilang, Lintong, and Gayo has low-acidity since it is processed using the wet-hulling method. Robusta coffee is grown in the lowlands while Arabica is in the highlands. The island is the leading producer of Indonesian coffee in the country. Sumatra is quite significant to the country because it produces petroleum and palm oil. There are about 52 languages in Sumatra, but like in the other parts of Indonesia, the official language of the island is Indonesian. Islam is the main religion in Sumatra with 87.1% of the locals being Muslims. North Sumatra had an estimated population of about 13,527,937 people in 2014. The island is divided into ten administrative regions with the North Sumatra being the most populous administrative region. Sumatra is one of the world’s most populous islands with over 50 million residents and a population density of about 272 individuals per square mile. The western part of the island is mountainous while the eastern part is swampy plains. The island is situated on the Ring of Fire and thus volcanic in nature with the Great Sumatran Fault and the Sundra megathrust spanning the west coast. The southeast-northwest axis is the longest axis on the island (1,110 miles) which crosses the equator while the widest part is about 270 miles. Sumatra is situated in the Indian Ocean and is separated from the Malay Peninsula by the Strait of Malacca and the islands of Java and Borneo by the Sunda Strait and Karimata Strait respectively. The island was referred to as Swarnabhumi in the past due to the presence of gold in the region meaning 'land of gold.' The island was named 'Sumatra' by Marco Polo during the late-fourteenth century. Sumatra is one of the over 14,000 islands of the Southeast Asian nation of Indonesia. It is one of the Greater Sunda Islands of the Malay Archipelago. Sumatra is the sixth-biggest island on the planet occupying an area of approximately 182,812sq miles.