Northeastern Thailand or Isan consists of 20 provinces in northeastern Thailand. Isan is Thailand's largest region, on the Khorat Plateau, bordered by the Mekong River to the north and east, by Cambodia to the southeast and the Sankamphaeng Range south of Nakhon Ratchasima. To the west it is separated from northern and central Thailand by the …Northeastern Thailand or Isan consists of 20 provinces in northeastern Thailand. Isan is Thailand's largest region, on the Khorat Plateau, bordered by the Mekong River to the north and east, by Cambodia to the southeast and the Sankamphaeng Range south of Nakhon Ratchasima. To the west it is separated from northern and central Thailand by the Phetchabun Mountains. Isan covers 167,718 km², making it about half the size of Germany and roughly the size of England and Wales. The total forest area is 25,203 km² or 15 percent of Isan's area.