Answer:
If you are using them for navigation, they can show you where easier paths might be.
They show us natural water features that we can use to find our way. Water features are in blue. Direction of stream travel can be determined by how the stream encounters the contour lines; the contour lines point upstream. In the example below, the stream runs from east (right) to west (left). The green arrow points at the head of the stream.
Hope this helps
