Cambodia,[a] officially the Kingdom of Cambodia,[b] is a country in Mainland Southeast Asia. It is bordered by Thailand to the northwest, Laos to the north, and Vietnam to the east, and has a coastline along the Gulf of Thailand in the southwest. It spans an area of 181,035 square kilometres (69,898 square miles), dominated by a low-lying plain and the confluence of the Mekong river and Tonlé Sap, Southeast Asia's largest lake. It is dominated by a tropical climate. Cambodia has a population of about 17 million people,[8] the majority of which are ethnically Khmer. Its capital and most populous city is Phnom Penh, followed by Siem Reap and Battambang.[15]  Traditionally, the Khmer people have a recorded information on Tra leaves. Tra leaf books record legends of the Khmer people, the Ramayana, the origin of Buddhism and other prayer books. They are taken care of by wrapping in cloth to protect from moisture and the climate.[257] Bon Om Touk (Cambodian Water & Moon Festival), the annual boat rowing contest, is the most attended Cambodian national festival. Held at the end of the rainy season when the Mekong River begins to sink back to its normal levels allowing the Tonle Sap River to reverse flow, approximately 10% of Cambodia's population attends this event each year to play games, give thanks to the moon, watch fireworks, dine, and attend the boat race in a carnival-type atmosphere.[258]