Thank you for your response, Ok that explains why the area and volume are different, what I was really struggling with was why is the 2d surface area not the same. When I calculate these statistics for the lake (depth expressed in positive numbers) the plane would be set to 0 and I would be �??calculating above the line�?�, however, that 2d surface area does not match up with the area calculated with the field calculator, it is the �??calculate below the line�?� 2d surface area that matches up with the field calculator. In the image you posted above the blue line would represent your 2d surface area and it remains consistent regardless of the above/below calculation, or am I mistaken on this point?