The invention discloses a method for measuring positions of structures on a mask and thereby determining mask manufacturing errors. It is shown, that from a plurality measurement sites an influence of an optical proximity effect on a position measurement of structures on the mask, is determined with a metrology tool. A rendered image of the data representation of the structures is obtained. Additionally, at least one optical image of the pattern within the area on the mask is captured with the imaging system of the metrology tool. The field of view of the metrology tool is approximately identical to the size of the selected area of the mask design data. Finally, a residual is determined, which shows the manufacturing based proximity effect.