US dollar. Thailand was the most visited country in Southeast Asia in 2013, according to the World Tourism Organisation. Estimates of tourism receipts directly contributing to the Thai GDP of 12 trillion baht range from 9 percent (1 trillion baht) (2013) to 16 percent. When including the indirect effects of tourism, it is said to account for 20.2 percent (2.4 trillion baht) of Thailand's GDP. Asian tourists primarily visit Thailand for Bangkok and the historical, natural, and cultural sights in its vicinity. Western tourists not only visit Bangkok and surroundings, but in addition many travel to the southern beaches and islands. The north is the chief destination for trekking and adventure travel with its diverse ethnic minority groups and forested mountains. The region hosting the fewest tourists is Isan. To accommodate foreign visitors, a separate tourism police with offices were set up in the major tourist areas and an emergency telephone number. Thailand ranks fifth biggest medical tourism destination of inbound medical tourism spending, according to World Travel and Tourism Council, attracting over 2.5 million visitors in 2018. The country is also Asia's number one. The country is popular for the growing practice of sex reassignment surgery (SRS) and cosmetic surgery. In 2010–2012, more than 90% of medical tourists travelled to Thailand for SRS. Prostitution in Thailand and sex tourism also form a de facto part of the economy. Campaigns promote Thailand as exotic to attract tourists. One estimate published in 2003 placed the trade at US$4.3 billion per year or about 3% of the Thai economy. It is believed that at least 10% of tourist dollars are spent on the sex trade. Agriculture and natural resources Forty-nine per cent of Thailand's labour force is employed in agriculture. This is down from 70% in 1980. Rice is the most important crop in the country and Thailand had long been the world's leading exporter of rice, until recently falling behind both India and Vietnam. Thailand has the highest percentage of arable land, 27.25%, of any nation in the Greater Mekong Subregion. About 55% of the arable land area is used for rice production. Agriculture has been experiencing a transition from labour-intensive and transitional methods to a more industrialised and competitive sector. Between 1962 and 1983, the agricultural sector grew by 4.1% per year on average and continued to grow at 2.2% between 1983 and 2007. The relative contribution of agriculture to