Why are there differences in the shape area and shape length fields for the same feature stored in a file geodatabase versus an enterprise geodatabase?

Answer

When new feature classes are created within a geodatabase, fields are added and maintained that store the shape length values for polyline feature classes and the shape length and area values for polygon feature classes. In file geodatabases, these fields are called Shape_Length and Shape_Area. In enterprise geodatabases, the names of these fields are dependent on the underlying DBMS. For the purpose of this article, the fields are referred to as Shape_Length and Shape_Area.

The values stored within the Shape_Length and Shape_Area fields are dependent on the characteristics of each feature's geometry and the geometry storage type for the feature class. When values of the Shape_Length and Shape_Area for the same feature stored within different geodatabase types and using different geometry storage types are compared, small differences can occur if the geometry contains parametric curves.

Enterprise geodatabases support the storage of both densified lines, and parametric curves. However, the values returned in the Shape_Area and Shape_Length fields are based on the measurement of the densified line. 

File geodatabases also support the storage of parametric curves and use the ArcObjects-based geometry engine for populating the Shape_Length and Shape_Area fields. This will base the measurement on a parametric curve if it is present. The difference in how these values are calculated is what causes the slight discrepancies in the Shape_Length and Shape_Area fields when comparing data stored in file geodatabases with enterprise geodatabases. The amount of discrepancy is entirely dependent on the number and characteristics of the parametric curves in the geometry.

There are a variety of methods to determine the area and length of enterprise geodatabase geometries containing parametric curves.

• Attribute Rules
• Calculate Geometry
• Calculate Features
• Attribute Assistant

For land records applications, we do not recommend using the values in the Shape_Area or Shape_Length fields because of the discrepancy described above and due to the fact that the legal area of a parcel as specified on a survey can differ slightly from the calculated area of the parcel.