Riau is a province of Indonesia. It is located in the central eastern coast of Sumatra along the Strait of Malacca. Until 2004 the province included the offshore Riau Islands, a large group of small islands (of which the principal islands are Batam and Bintan) located east of Sumatra Island and south of Singapore, before these islands were split off as a province in July 2004. The provincial capital and the largest city of Riau is Pekanbaru. The province shares land borders with North Sumatra to the northwest, West Sumatra to the west, and Jambi to the south. The total area for Riau province is , which stretches from the slopes of the Bukit Barisan to the Strait of Malacca. Riau has a wet tropical climate with average rainfall ranging between 2000 and 3000 millimeters per year, and the average rainfall per year is about 160 days. Riau is currently one of the richest provinces in Indonesia and is rich in natural resources, particularly petroleum, natural gas, rubber, palm oil and fibre plantations. Extensive logging and plantation development in has led to a massive decline in forest cover Riau, and associated fires have contributed to haze across the larger region. Riau is considered part of the Malay world. It is currently considered as the cultural center of the Malays in Indonesia. Nevertheless, Riau is considered a very diverse province, as it is inhabited by many ethnic groups, such as Malay, Minangkabau, Chinese and Batak. The local Riau dialect of Malay is considered as the "lingua franca" in the province, but Indonesian, the standardized form of Malay is used as the official language and also as the second language of many people. Other than that, different languages such as Minangkabau, Hokkien and varieties of Batak languages are also spoken.