I have a shapefile with 62.000 polygons.

I have created two fields (Double) AREA1 and AREA2 with identical properties.

On **AREA1** I have calculated the area of polygons with Calculate Geometry > area process.

On **AREA2** I have calculated the area of polygons with Field calculator and the command: !shape.area!

When I compare the difference between the two fields ([AREA1] - [AREA2]), I find 30 polygons with no zero difference less than 0,01 square meters.

Is there a different algorithm for these processes?

Does anyone know why is this happening?

does the file have a defined coordinate system? problems in calculating shape geometry arise when there is no know coordinate system. This is well documented on this site.