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We have self developed application based on ArcGIS 9.3.1 SP2. Our agents use that application to edit parcels. The parcel layer has a field SHAPE_AREA that is calculated by ArcGIS. Our application gets the value of the field property to show the area of the parcel. However we see now that the area is not always correct. The most flagrant difference we encountered was an area of 17ca (m²) instead of 29ca. I try to find out why the values are not correct and how many of those values are incorrect. To do that I open the shapefile in ArcGIS 10.2.1. and I add a field named "area2" with the same properties as the field SHAPE_AREA (type: double, number format: numeric, precision: 11, scale:4), I use Calculate Geometry to get the area and i use the same projection. Then I add a field named "result" with the same properties. I calculate the field: SHAPE_AREA - area2 to get the differences.

result

Can anybody tell me why I get different results when both calculations are done by ArcGIS on fields with the same properties? And how we can resolve this problem?

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    You say that you have a field "SHAPE_AREA" that is calculated by ArcGIS but you do not tell us how that happens other than that you are using a "self developped application based on ArcGIS 9.3.1 SP2". Would you be able to edit your question to describe how you eliminated what happens in that application from suspicion of being the cause, please? – PolyGeo Oct 9 '15 at 10:02
  • That's a good question PolyGeo. I will ask our developper how the application calculates the value and then I can edit my question. – Filip Cooreman Oct 9 '15 at 11:35
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    Be sure to specify the coordinate system of the data layer. – Vince Oct 9 '15 at 13:39
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    Are you working with a shapefile or a geodatabase feature class? The shapefile can have a field named Shape_Area (which can easily happen if it came from a feature class) but it will not update automatically so every time it is edited you have to recalculate. The feature class has to have a Shape_Area field and that is supposed to update. – johns Oct 9 '15 at 13:43
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The problem is with your self developped application. From your snapshot I can tell you are using a shapefile (it includes FID field and not OBJECTID); you also indicated in the body of your question. So the SHAPE_AREA field is created and populated by yourself.

Note that If you create a polygon inside a FileGeodatabase, Shape_AREA gets created (it is part of geodatabase functionality).

So to solve this situation, either use FileGeodatabase to store your featureclasses or post the sample code of the developed application in another question.

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    While your assumption is probably true, seeing the FID field does not mean OP is using a shapefile. You can alias the OID field (or any field for that matter) to display pretty much anything. – Paul Oct 9 '15 at 19:31
  • You are right. But it increases the probability of being shapefile. Furthermore the OP mentions shapefile in its question. – Farid Cheraghi Oct 9 '15 at 19:33
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    Indeed, we are using shapefiles. The application was created in 2005 based on ArcObjects within ArcGIS 8.3. In that version we never had this specific problem. The application was reprogrammed a few years ago based on ArcGIS 9.3.1SP2. The problem has to be in the programming code of this version. I will ask the programmer to look into the code and find out at which moment the Area gets calculated and which parameters are used. – Filip Cooreman Oct 11 '15 at 6:25

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