Classification of streams within a drainage basin so that it can be compared with another. Different methods have been proposed with strahler being most common. From a source to a confluence, a stream is considered 1st order. When two 1st order steams join, the resultant stream is a 2nd order stream. Where two 2nd order streams join a 3rd is created and so on. When streams of different orders join, the resultant stream remains as the higher order of the two that came together.