Why do people use the terms upper, middle, and lower course when talking about the route of a river?

Question

I have no idea...

Answer 1

Such designation is a better alternative than using directional terms like North and South. A river may zigzag and meander. But referring to the river mouth as the lower course gets around this problem. Remember too that rivers flow downhill, so it makes sense that in speaking of rivers one refers to its upper and lower portion.