Why would geographers want to make a map of where pollutants travel in a river?

First of all, scientists often make maps and models just for the sake of knowledge - so that we have a better understanding of the world around us.

Second, such a map could give us valuable information about the river currents.

But lastly, and perhaps most important of all, such a map could help us understand which parts of the river are dangerous to health - for example to swimming or fishing

Afine-grained igneous rock forms as a result of slow cooling.