In a topographic map, why would a lake or body of water not have any contour lines on its surface?

Contour lines do not show up on a lake or a body of water because each line corresponds to a specific elevation, and contour lines never cross each other such as mountains and valleys. COntour lines that are in topographic maps are imaginary lines that connect different point of equal elevation above a reference level, which usually means at sea level.

The us is first  the  u.s. economy  remains the  largest in the world  in terms of nominal  gdp. however, the  u.s. economy  loses its spot as the number one  economy  to china when  measured  in terms of  gdp  based on ppp. in these terms, china's  gdp  is $23.19 trillion exceeds the  u.s. gdp  of $19.42 trillion