The average elevation is 200m and it covers an area of about 155,000 km². The saucer-shaped plateau is tilted towards the south-east, and is drained by the Mun and Chi rivers, tributaries to the Mekong, which also is the boundary of the area. It is separated from Central Thailand by the Phetchabun mountain range, and to the south from Cambodia by the Dongrek mountains.
These together with the Truong Son Cordilliera in the north-east catch a lot of the rainfall, so the South-West monsoon has much lower intensity then in other regions - the mean annual rainfall in Nakhon Ratchasima is about 1150mm, compared with 1500mm in Central Thailand. The difference between dry and wet season is much stronger, which makes the area less fertile for rice.