Answer the following question given this paragraph: 

Indeed, scientists discovered something astonishing. Many times in Earth’s history, the magnetic poles have switched positions. North becomes south and south becomes north! When the north and south poles are aligned as they are now, geologists say it is normal polarity. When they are in the opposite position, they say that it is reversed polarity.


Q: What feature of the land do contour lines show?


A:
three-dimensional shape