Different between Shape area and calculate geometry

Question

HI

I have a feature class in an SDE geodatabase but the shape area is different if I compare it to a calculated area (using the tool Calculate Geometry (area field).  Shouldn't it be the same area?

If the feature class is in file geodatabase the shape area field = area field

Hope I have an answer

Thanks

Greta

JoshuaBixby · Answer

@SterlingLoetz, see my reply on your other discussion.

SterlingLoetz · Answer

I am experiencing the same issue here: Feature Geometry Calculated In ArcGIS Pro vs SQL Server

"I need help understanding the difference in feature geometry area calculations in an SQL Server sde geodatabase vs calculated area values in ArcGIS Pro via the calculate geometry tool.

I have a feature class with impervious areas within an sql sde geodatabase. The area geometry field automatically added to the feature class upon creation is Shape.STArea(). The dataset uses the Colorado State Plane Central (Feet) coordinate system.

I added two additional fields, Planer Sqft & Geodesic Sqft, and calculated their geometries using the Calculate Geometry gp tool using the Planer or Geodesic method respectively in square feet. See the image for example values.

I understand the difference between the calculated geodesic value and planer value. I do not understand how the Shape.STArea() geometry field is calculated. Shouldn't this value be the same as either the planer or geodesic values? Is there another method that sql uses to calculate area geometry values? The difference in this case between the STArea() and Planer values is about 9.86. The amount of discrepancy seems to be related to polygon size.

In terms of best practices, which values is more accurate and should be used, the sql STArea() or the calculated area value in ArcGIS Pro?"

JoshuaBixby · Answer

Given this is an enterprise geodatabase (EGDB/SDE) it is important to state what back-end DBMS you are using and whether the data is versioned or not.