Why do the contour of different heights not cross each other?

How do the contour lines show the direction of the flow of rivers and streams?

Complete the following by drawing the conventional sign/symbol in the blank boxes:

Draw conventional symbols for the following using appropriate colours where necessary.

(i) Cart-track

(ii) Broken ground

(iii) Nala

(iv) Perennial tank

(v) Stream

(vi) Dry-stream