STGeometryType (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
SQL database in Microsoft Fabric
Returns the Open Geospatial Consortium (OGC) type name represented by a geometry instance.
Syntax
.STGeometryType ( )
Return Types
SQL Server return type: nvarchar(4000)
CLR return type: SqlString
Remarks
The OGC type names that can be returned by STGeometryType() are Point, LineString, CircularString, CompoundCurve, Polygon, CurvePolygon, GeometryCollection, MultiPoint, MultiLineString, and MultiPolygon.
Examples
The following example creates a Polygon instance and uses STGeometryType() to confirm that it is a polygon.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('POLYGON((0 0, 3 0, 3 3, 0 3, 0 0))', 0);
SELECT @g.STGeometryType();