* a given contour line is ALWAYS at the same elevation.

* two different contour lines cannot cross.

* the closer contour lines are to each other, the steeper the topography; the farther apart they are, the gentler the topography.

* contour lines are wiggly because the landscape is typically irregular.  --> Contour lines always  make "Vs" which point up valleys.

* closed contour lines represent hilltops.
 

Make sure you understand these points!