way to get area of any simple polygon

Pick's theorem

this theorem give us a simple formula for calculating the area of any simple polygon constructed on a grid of equal-distanced points. 

i =interior points located in the polygon

b=boundary points placed on the polygon's perimeter

example : In this simple polygon constructed on a grid of equal-distanced points then i = 39 (interior points located in the polygon) and b = 14(boundary points placed on the polygon's perimeter) then

A =  39 + 14/2   -1 = 45 square units

example 2 :  in this simple polygon constructed on a grid of equal-distanced points 

i = 5 and b = 7 then A = 5 + 7/2 - 1 = 7.5 square units