Kaw Yao Yai is an island about 26 kilometres long and 7 kilometres broad at it widest, but in most places it is much narrower than this. Its surface is very hilly. The hills, which are of nogreat height, are usually rounded in out line and composed of sandstone and shale. A few small perennial streams run down from these hills. There are several small villages on the island, all of them on or near the coast.