The modern municipality dates to a sanitary district (sukhaphiban) that was created in 1915. This was upgraded to a municipality (thesaban) on March 29, 1935, as published in the Royal Gazette, Book No. 52 section 80. First covering just 17.5 km2 (7 sq mi), the city was enlarged to 40.216 km2 (16 sq mi) on April 5, 1983.[15]