InstanceOf (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
A method that tests if the geometry instance is the same as the specified type. Returns 1 if the type of a geometry instance is the same as the specified type. This method also returns 1 if the specified type is an ancestor of the instance type. Otherwise, this method returns 0.
Syntax
.InstanceOf (geometry_type )
Arguments
geometry_type
nvarchar(4000) string specifying one of 15 types exposed in the geometry type hierarchy.
Return Types
SQL Server return type: bit
CLR return type: SqlBoolean
Remarks
The input for the method must be one of the following types: Geometry, Point, Curve, LineString, CircularString, CompoundCurve, Surface, Polygon, CurvePolygon, GeometryCollection, MultiSurface, MultiPolygon, MultiCurve, MultiLineString, and MultiPoint. This method throws an ArgumentException if any other strings are used for the input.
Examples
The following example creates a MultiPoint instance and uses InstanceOf() to see if the instance is a GeometryCollection.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('MULTIPOINT(0 0, 13.5 2, 7 19)', 0);
SELECT @g.InstanceOf('GEOMETRYCOLLECTION');