Any element can always be identified by its: atomic mass
number of neutrons
number of protons
atomic number

Explanation:

atomic mass

Really...i think it can also be atomic number..

in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

explanation: