error in the calculation of surfaces

[Giovannino60]

I have made polylines and then I have inserted a retino, with property, retino comes for example 1114.49 square meters and instead making calculation area with the calculator ie base for height or with the instrument measure exits area 596.6188 square meters?

Thank you.

 

[dieva]

the retino of which melts the area is a retino that also contemplates the areas of the 3 buildings on the lower right and not only the rectangle that you measured.
a single retino was created by selecting 4 closed areas.