STSymDifference (geography Data Type)
Returns an object that represents all points that are either in one geography instance or another geography instance, but not those points that lie in both instances.
This method always returns null if the spatial reference identifiers (SRIDs) of the geography instances do not match.
SQL Server supports spatial instances that are larger than a hemisphere. In SQL Server, the set of possible results on the server has been extended to FullGlobe instances.
The result may contain circular arc segments only if the input instances contain circular arc segments.
A. Computing the symmetric difference of two polygons
The following example uses STSymDifference() to compute the symmetric difference of two Polygon instances.
DECLARE @g geography; DECLARE @h geography; SET @g = geography::STGeomFromText('POLYGON((-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))', 4326); SET @h = geography::STGeomFromText('POLYGON((-122.351 47.656, -122.341 47.656, -122.341 47.661, -122.351 47.661, -122.351 47.656))', 4326); SELECT @g.STSymDifference(@h).ToString();
B. Computing the symmetric difference with FullGlobe
The following example compares the symmetric difference of a Polygon with FullGlobe.
DECLARE @g geography = 'POLYGON((-122.358 47.653, -122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))';