Bangkok is situated in the Chao Phraya River delta in Thailand's central plains. The river meanders through the city in a southward direction, emptying into the Gulf of Thailand approximately 25 kilometres (16 mi) south of the city centre.
The area is Flat and low-lying, with an average elevation of 1.5 metres (4 ft 11 in) above sea level.
Most of the area was originally swampland, which was gradually drained and irrigated for agriculture via the construction of canals (khlong) which took place throughout the sixteenth to sixteenth centuries.
The course of the river as it flows through Bangkok has been modified by the construction of several shortcut canals.