Bangkok is on the lower of Chao Phraya River bank. It's situated on the central plain that had been built from the eroded topsoils of mountains in the north of the country for million years. With time, the eroded mountain soils had flowed into the sea by the Chao Phraya River and built an alluvial fan delta layer by layer that eventually became the central plain that would be an extremely fertile land.

In Bangkok, the land stands only 1-2 meters above sea level.