A drainage basin is the area that encompasses all the land from which water flows into a particular stream or river. Stream is a synonym of river, and although typically something called a stream is smaller than a river, here, any flowing body of water in a clearly defined channel will be called a stream. The size of a drainage basin can vary from being as small as a few square miles or kilometers to as large as part of a continent. An example of a divide is the continental divide of North America, which separates streams that ultimately empty into one ocean (the Pacific Ocean) from those that ultimately empty into another (the Gulf of Mexico). The smallest streams in any particular area are called first order streams, and the land from which water flows into a particular first...