Answer:
Elevation of Zero feet, Means
If represented on number line , it is in middle of Number line equidistant from both sides.
=At sea level
→Integer={------,-3,-2,-1,0,1,2,3,..............},
0 is in the middle of integers, that means neither positive nor negative.
→Elevation above Zero Feet=Positive Integer
→Elevation below Zero Feet=Negative Integer